This commit rewrites the function dispatcher code to support mixing
regular arguments with py::args/py::kwargs arguments.  It also
simplifies the argument loader noticeably as it no longer has to worry
about args/kwargs: all of that is now sorted out in the dispatcher,
which now simply appends a tuple/dict if the function takes
py::args/py::kwargs, then passes all the arguments in a vector.

When the argument loader hit a py::args or py::kwargs, it doesn't do
anything special: it just calls the appropriate type_caster just like it
does for any other argument (thus removing the previous special cases
for args/kwargs).

Switching to passing arguments in a single std::vector instead of a pair
of tuples also makes things simpler, both in the dispatch and the
argument_loader: since this argument list is strictly pybind-internal
(i.e. it never goes to Python) we have no particular reason to use a
Python tuple here.

Some (intentional) restrictions:
- you may not bind a function that has args/kwargs somewhere other than
  the end (this somewhat matches Python, and keeps the dispatch code a
  little cleaner by being able to not worry about where to inject the
  args/kwargs in the argument list).
- If you specify an argument both positionally and via a keyword
  argument, you get a TypeError alerting you to this (as you do in
  Python).

Adds a 32-bit (debian) build to travis-ci.

* Abstract away some holder functionality (resolve #585)

Custom holder types which don't have `.get()` can select the correct
function to call by specializing `holder_traits`.

* Add support for move-only holders (fix #605)

* Clarify PYBIND11_NUMPY_DTYPE documentation

The current documentation and example reads as though
PYBIND11_NUMPY_DTYPE is a declarative macro along the same lines as
PYBIND11_DECLARE_HOLDER_TYPE, but it isn't.  The changes the
documentation and docs example to make it clear that you need to "call"
the macro.

* Add satisfies_{all,any,none}_of<T, Preds>

`satisfies_all_of<T, Pred1, Pred2, Pred3>` is a nice legibility-enhanced
shortcut for `is_all<Pred1<T>, Pred2<T>, Pred3<T>>`.

* Give better error message for non-POD dtype attempts

If you try to use a non-POD data type, you get difficult-to-interpret
compilation errors (about ::name() not being a member of an internal
pybind11 struct, among others), for which isn't at all obvious what the
problem is.

This adds a static_assert for such cases.

It also changes the base case from an empty struct to the is_pod_struct
case by no longer using `enable_if<is_pod_struct>` but instead using a
static_assert: thus specializations avoid the base class, POD types
work, and non-POD types (and unimplemented POD types like std::array)
get a more informative static_assert failure.

* Prefix macros with PYBIND11_

numpy.h uses unprefixed macros, which seems undesirable.  This prefixes
them with PYBIND11_ to match all the other macros in numpy.h (and
elsewhere).

* Add long double support

This adds long double and std::complex<long double> support for numpy
arrays.

This allows some simplification of the code used to generate format
descriptors; the new code uses fewer macros, instead putting the code as
different templated options; the template conditions end up simpler with
this because we are now supporting all basic C++ arithmetic types (and
so can use is_arithmetic instead of is_integral + multiple
different specializations).

In addition to testing that it is indeed working in the test script, it
also adds various offset and size calculations there, which
fixes the test failures under x86 compilations.

fixed VS build, when _DEBUG is just defined without any value assigned (e.g. VS15)

* Make 'any' the default markup role for Sphinx docs

* Automate generation of reference docs with doxygen and breathe

* Improve reference docs coverage

* Some clarifications to section on virtual fns

Primarily, I made it clear that PYBIND11_OVERLOAD_PURE_NAME is not "useful" but required in renaming situations. Also clarified that one should not bind to the trampoline helper class which I found tempting since it seems more explicit.

* Remove :emphasize-lines: from cpp block, seems to suppress formatting

* docs: emphasize default policy, clarify keep_alive

Emphasize the default return value policy since this statement is hidden in a wall of text. 

Add a hint that call policies are probably required for container objects.

* [Doc] Fix several errors of examples from the doc

* Add missing operator def.

* Added missing `()`

* Add missing `namespace`.

Correct function signature of module init function generated PYBIND11_PLUGIN_IMPL macro for Python 2.x (#602)

This way a non-CACHE variable can also be used. For example:
```
set(PYBIND11_PYTHON_VERSION <value>)
add_subdirectory(...)
```

On a debian jessie machine, running 'python --version --noconftest' caused
pytest to try and run the test suite with the not-yet-compiled extension
module, thus failing the test. This commit chages the pytest detection
so that it only attempts to run an import statement.

Both are no longer needed: debian testing has Python 2.7.13 final now,
and wheels of numpy and scipy are available.

Fixes #567.

If pybind's CMakeLists gets loaded via an include_directory from another
CMakeLists with a higher minimum version (e.g. 3.0), the project()
command without a version produces a CMP0048 warning.

This commit explicitly requests the new behaviour if the policy exists,
as it won't cause problems (we set VERSION later).

* Fixed a regression that was introduced in the PyPy patch: use ht_qualname_meta instead of ht_qualname to fix PyHeapTypeObject->ht_qualname field.

* Added a qualname/repr test that works in both Python 3.3+ and previous versions

* Temporarily allows osx homebrew Python 3.6 to fail.

https://github.com/pybind/pybind11/pull/570#issuecomment-269120613

"Homebrew just got Python 3.6 (brew install python3), but numpy and scipy don't have binary wheels for 3.6 yet so it's trying to compile from source and failing."

Makes room for an eventual pybind11::embedded target.

See the documentation for a description of the options.

Add a BUILD_INTERFACE and a pybind11::pybind11 alias for the interface
library to match the installed target.

Add new cmake tests for add_subdirectory and consolidates the
.cpp and .py files needed for the cmake build tests:

Before:
tests
|-- test_installed_module
|   |-- CMakeLists.txt
|   |-- main.cpp
|   \-- test.py
\-- test_installed_target
    |-- CMakeLists.txt
    |-- main.cpp
    \-- test.py

After:
tests
\-- test_cmake_build
    |-- installed_module/CMakeLists.txt
    |-- installed_target/CMakeLists.txt
    |-- subdirectory_module/CMakeLists.txt
    |-- subdirectory_target/CMakeLists.txt
    |-- main.cpp
    \-- test.py