Catch v2 changed the `run(...)` signature to take a `char *argv[]`,
arguing partly that technically a `char *argv[]` type is the correct
`main()` signature rather than `const char *argv[]`.

Dropping the `const` here doesn't appear to cause any problems with
catch v1 (tested against both the cmake-downloaded 1.9.3 and Debian's
1.12.1 package) so we can follow suit.

* stl.h: propagate return value policies to type-specific casters

Return value policies for containers like those handled in in 'stl.h'
are currently broken.

The problem is that detail::return_value_policy_override<C>::policy()
always returns 'move' when given a non-pointer/reference type, e.g.
'std::vector<...>'.

This is sensible behavior for custom types that are exposed via
'py::class_<>', but it does not make sense for types that are handled by
other type casters (STL containers, Eigen matrices, etc.).

This commit changes the behavior so that
detail::return_value_policy_override only becomes active when the type
caster derives from type_caster_generic.

Furthermore, the override logic is called recursively in STL type
casters to enable key/value-specific behavior.

Switching deprecated Thread Local Storage (TLS) usage in Python 3.7 to Thread Specific Storage (TSS) (#1454)

* Switching deprecated Thread Local Storage (TLS) usage in Python 3.7 to Thread Specific Storage (TSS)

* Changing Python version from 3.6 to 3.7 for Travis CI, to match brew's version of Python 3

* Introducing PYBIND11_ macros to switch between TLS and TSS API

The current code requires implicitly that integral types are cast-able to floating point. In case of strongly-typed integrals (e.g. as explained at http://www.ilikebigbits.com/blog/2014/5/6/type-safe-identifiers-in-c) this is not always the case.

This commit uses SFINAE to move the numeric conversions into separate `cast()` implementations to avoid the issue.

* Silence GCC8's -Wcast-function-type.

See https://bugs.python.org/issue33012 and PRs linked therein.

It is useful not only to remember the python libs and includes but
also the interpreter version in cache.

If users call pybind11 throught `add_subdirectories` they will
otherwise have no access to the selected interpreter version.
The interpreter version is useful for downstream projects, e.g.
to select default `lib/pythonX.Y/site-packages/` install paths.

Add missing python3 distutils on Debian "buster".

If an exception is thrown during module initialization, the
error_already_set destructor will try to call `get_internals()` *after*
setting Python's error indicator, resulting in a `SystemError: ...
returned with an error set`.

Fix that by temporarily stashing away the error indicator in the
destructor.

Fixes #1401

Fixed typos (erroneous `;`) in `classes.rst`.

Fix a segfault when creating a 0-dimension, c-strides array.

Found via `codespell`

When using pybind11 to bind enums on MSVC and warnings (/W4) enabled,
the following warning pollutes builds. This fix renames one of the
occurrences.

pybind11\include\pybind11\pybind11.h(1398): warning C4459: declaration of 'self' hides global declaration
pybind11\include\pybind11\operators.h(41): note: see declaration of 'pybind11::detail::self'

* Add basic support for tag-based static polymorphism

Sometimes it is possible to look at a C++ object and know what its dynamic type is,
even if it doesn't use C++ polymorphism, because instances of the object and its
subclasses conform to some other mechanism for being self-describing; for example,
perhaps there's an enumerated "tag" or "kind" member in the base class that's always
set to an indication of the correct type. This might be done for performance reasons,
or to permit most-derived types to be trivially copyable. One of the most widely-known
examples is in LLVM: https://llvm.org/docs/HowToSetUpLLVMStyleRTTI.html

This PR permits pybind11 to be informed of such conventions via a new specializable
detail::polymorphic_type_hook<> template, which generalizes the previous logic for
determining the runtime type of an object based on C++ RTTI. Implementors provide
a way to map from a base class object to a const std::type_info* for the dynamic
type; pybind11 then uses this to ensure that casting a Base* to Python creates a
Python object that knows it's wrapping the appropriate sort of Derived.

There are a number of restrictions with this tag-based static polymorphism support
compared to pybind11's existing support for built-in C++ polymorphism:

- there is no support for this-pointer adjustment, so only single inheritance is permitted
- there is no way to make C++ code call new Python-provided subclasses
- when binding C++ classes that redefine a method in a subclass, the .def() must be
  repeated in the binding for Python to know about the update

But these are not much of an issue in practice in many cases, the impact on the
complexity of pybind11's innards is minimal and localized, and the support for
automatic downcasting improves usability a great deal.

The property returns the enum_ value as a string.
For example:

>>> import module
>>> module.enum.VALUE
enum.VALUE
>>> str(module.enum.VALUE)
'enum.VALUE'
>>> module.enum.VALUE.name
'VALUE'

This is actually the equivalent of Boost.Python "name" property.

As reported in #1349, clang before 3.5 can segfault on a function-local
variable referenced inside a lambda.  This moves the function-local
static into a separate function that the lambda can invoke to avoid the
issue.

Fixes #1349

I think that there's the word "for" missing for that sentence to be correct.
Please double-check that the sentence means what it's supposed to mean. :-)

This reimplements the version check to avoid sscanf (which has
reportedly started throwing warnings under MSVC, even when used
perfectly safely -- #1314).  It also extracts the mostly duplicated
parts of PYBIND11_MODULE/PYBIND11_PLUGIN into separate macros.

- PYBIND11_MAKE_OPAQUE now takes ... rather than a single argument and
  expands it with __VA_ARGS__; this lets templated, comma-containing
  types get through correctly.
- Adds a new macro PYBIND11_TYPE() that lets you pass the type into a
  macro as a single argument, such as:

      PYBIND11_OVERLOAD(PYBIND11_TYPE(R<1,2>), PYBIND11_TYPE(C<3,4>), func)

  Unfortunately this only works for one macro call: to forward the
  argument on to the next macro call (without the processor breaking it
  up again) requires also adding the PYBIND11_TYPE(...) to type macro
  arguments in the PYBIND11_OVERLOAD_... macro chain.
- updated the documentation with these two changes, and use them at a couple
  places in the test suite to test that they work.

Apparently with homebrew the correct package for python3 is now just
`python`; python 2 was relegated to 'python@2', and `python3` is an
alias for `python` (which needs to be upgraded rather than installed).

This fixes the test code on big-endian architectures: the array support
(PR #832) had hard-coded the little-endian '<' but we need to use '>' on
big-endian architectures.