Genpybind

Enhancements

* Snapshot tests based on pydoc have been added. For each test target, a
text-only documentation is generated that contains a description of the
contained modules, classes, functions and methods, their default arguments and
docstrings etc. This documentation is compared to artifact files stored in
[`tests/expected`](./tests/expected).

Thanks to several contributors from the [Electronic Vision(s)
Group](https://github.com/electronicvisions) for patches,
documentation and helping to test this release!

Deprecations

* Support for running genpybind using Python 2.x will likely be dropped in the
next release.
* Use of the `--genpybind-tag` feature to limit which declarations are exposed
in a given module will only be allowed on a namespace granularity, by
applying `tag` or `tags` annotations to namespace definitions. Definitions
in nested namespaces will only be exposed if the enclosing namespace is
exposed.
* The `opaque` keyword will likely be renamed and/or undergo a redesign (see
[issue 24](https://github.com/kljohann/genpybind/issues/24)).

Enhancements

* Initial documentation has been added for the genpybind annotations and command
line arguments.
* It's now possible to specify the [holder
type](https://pybind11.readthedocs.io/en/stable/advanced/smart_ptrs.html#std-shared-ptr)
to use for a class using the `holder_type` annotation (see
[tests/holder_type.h](tests/holder_type.h)).
* A warning is now emitted at import time when a type alias references an
unknown or unexposed type.
* Type alias declarations are now supported (see [tests/typedefs.h](tests/typedefs.h)).
* `genpybind.h` is now copied to `${PREFIX}/include` when using `./waf
install`. It can still be useful to define compatible macros in a consuming
project instead, in order to use a different name for the macro or allow
compiling the library without an installed version of genpybind.
* The LLVM patches have been updated to match the LLVM 9.0 release.
* The test suite has been expanded.

Fixes

* Functions with `pybind::args` or `pybind::kwargs` parameters are now
wrapped properly.
* Sub-modules are no longer exposed when the enclosing namespace is not exposed.
* Cross-module aliases to nested types are now exposed correctly, as long as
the referred module is available at runtime.