When attempting to get a raw array pointer we return nullptr if given a
nullptr, which triggers an error_already_set(), but we haven't set an
exception message, which results in "Unknown internal error".

Callers that want explicit allowing of a nullptr here already handle it
(by clearing the exception after the call).

When processing many files that contain top-level items with the same
name (e.g. "operator<<"), the output was non-deterministic and depended
on the order in which the different Clang processes finished. This
commit adds sorting that also accounts for the filename to prevent
random changes from run to run.

(https://gitlab.kitware.com/cmake/cmake/issues/16783)

The 3.3.2 changelog indicates it has some VS 2017 fixes.  Updating to
see if that avoids the random build failures.

/m also doesn't seem to have made the builds any faster.

Many of the Eigen type casters' name() methods weren't wrapping the type
description in a `type_descr` object, which thus wasn't adding the
"{...}" annotation used to identify an argument which broke the help
output by skipping eigen arguments.

The test code I had added even had some (unnoticed) broken output (with
the "arg0: " showing up in the return value).

This commit also adds test code to ensure that named eigen arguments
actually work properly, despite the invalid help output.  (The added
tests pass without the rest of this commit).

The holder casters assume but don't check that a `holder<type>`'s `type`
is really a `type_caster_base<type>`; this adds a static_assert to make
sure this is really the case, to turn things like
`std::shared_ptr<array>` into a compilation failure.

Fixes #785

The gcc versions in Debian stretch (gcc 6) and experimental (gcc 7)
incorporate the upstream gcc fixes.

Fixes #775.

Assignments of the form `Type.static_prop = value` should be translated to
`Type.static_prop.__set__(value)` except when `isinstance(value, static_prop)`.

PR #771 deprecated them as they can cause linking failures (#770), but
the deprecation tags cause warnings on GCC 5.x through 6.2.x.  Removing
them entirely will break backwards-compatibility consequences, but the
effects should be minimal (only code that was inheriting from `object`
could get at them at all as they are protected).

Fixes #777

Besides appearing in the CMake GUI, the `:FILENAME` specifier changes
behavior as well:

cmake -DPYTHON_EXECUTABLE=python ..  # FAIL, can't find python
cmake -DPYTHON_EXECUTABLE=/path/to/python ..  # OK
cmake -DPYTHON_EXECUTABLE:FILENAME=python ..  # OK
cmake -DPYTHON_EXECUTABLE:FILENAME=/path/to/python ..  # OK

AppVeyor just added support for excluding specific jobs; thhis commit
cuts the number of builds down to 6 from 8 by eliminating the VS2015 x86
builds.

When make_tuple fails (for example, when print() is called with a
non-convertible argument, as in #778) the error message a less helpful
than it could be:

    make_tuple(): unable to convert arguments of types 'std::tuple<type1, type2>' to Python object

There is no actual std::tuple involved (only a parameter pack and a
Python tuple), but it also doesn't immediately reveal which type caused
the problem.

This commit changes the debugging mode output to show just the
problematic type:

    make_tuple(): unable to convert argument of type 'type2' to Python object

My group now has a subscription to AppVeyor pro, which also permits
running parallel builds on the open source projects.

```c++
m.def("foo", foo, py::call_guard<T>());
```

is equivalent to:

```c++
m.def("foo", [](args...) {
    T scope_guard;
    return foo(args...); // forwarded arguments
});
```

This commit adds `error_already_set::matches()` convenience method to
check if the exception trapped by `error_already_set` matches a given
Python exception type. This will address #700 by providing a less
verbose way to check exceptions.

* Support raw string literals as input for py::eval
* Dedent only when needed

The constexpr static instances can cause linking failures if the
compiler doesn't optimize away the reference, as reported in #770.

There's no particularly nice way of fixing this in C++11/14: we can't
inline definitions to match the declaration aren't permitted for
non-templated static variables (C++17 *does* allows "inline" on
variables, but that obviously doesn't help us.)

One solution that could work around it is to add an extra inherited
subclass to `object`'s hierarchy, but that's a bit of a messy solution
and was decided against in #771 in favour of just deprecating (and
eventually dropping) the constexpr statics.

Fixes #770.

* Arch-indep CMake packaging

Since pybind11 is a header-only library, the CMake packaging does not have to carry any architecture specific checks. Without this patch, the detection of pybind11 will fail on 32-bit architectures if the project was built on a 64-bit machine and vice-versa. This fix is similar to what is applied to `Eigen` and other header-only C++ libraries.

* nicer py::capsule destructor mechanism
* added destructor-only version of capsule & tests
* added documentation for module destructors (fixes #733)

We no longer need a nightly build now that 5.7 is released (and the
current nightly 5.8 is failing).

The extends the previous unchecked support with the ability to
determine the dimensions at runtime.  This incurs a small performance
hit when used (versus the compile-time fixed alternative), but is still considerably
faster than the full checks on every call that happen with
`.at()`/`.mutable_at()`.

This adds bounds-unchecked access to arrays through a `a.unchecked<Type,
Dimensions>()` method.  (For `array_t<T>`, the `Type` template parameter
is omitted).  The mutable version (which requires the array have the
`writeable` flag) is available as `a.mutable_unchecked<...>()`.

Specifying the Dimensions as a template parameter allows storage of an
std::array; having the strides and sizes stored that way (as opposed to
storing a copy of the array's strides/shape pointers) allows the
compiler to make significant optimizations of the shape() method that it
can't make with a pointer; testing with nested loops of the form:

    for (size_t i0 = 0; i0 < r.shape(0); i0++)
        for (size_t i1 = 0; i1 < r.shape(1); i1++)
            ...
                r(i0, i1, ...) += 1;

over a 10 million element array gives around a 25% speedup (versus using
a pointer) for the 1D case, 33% for 2D, and runs more than twice as fast
with a 5D array.

Fixes #754.

This extends the trivial handling to support trivial handling for
Fortran-order arrays (i.e. column major): if inputs aren't all
C-contiguous, but *are* all F-contiguous, the resulting array will be
F-contiguous and we can do trivial processing.

For anything else (e.g. C-contiguous, or inputs requiring non-trivial
processing), the result is in (numpy-default) C-contiguous layout.

The only part of the vectorize code that actually needs c-contiguous is
the "trivial" broadcast; for non-trivial arguments, the code already
uses strides properly (and so handles C-style, F-style, neither, slices,
etc.)

This commit rewrites `broadcast` to additionally check for C-contiguous
storage, then takes off the `c_style` flag for the arguments, which
will keep the functionality more or less the same, except for no longer
requiring an array copy for non-c-contiguous input arrays.

Additionally, if we're given a singleton slice (e.g. a[0::4, 0::4] for a
4x4 or smaller array), we no longer fail triviality because the trivial
code path never actually uses the strides on a singleton.

Instead of a segfault. Fixes #751.

This covers the case of loading a custom holder from a default-holder
instance. Attempting to load one custom holder from a different custom
holder (i.e. not `std::unique_ptr`) yields undefined behavior, just as
#588 established for inheritance.

py::arg() doesn't only specify named arguments anymore, so the error
message was misleading (e.g. when using `py::arg().noconvert()` and
forgetting `py::arg()` for a second positional argument).