Mebuex

Added
- Add the `mebuex_destpath` and `mebuex_destname` attributes to the
`MebuexExtension` class. This can be used from install scripts, after
performing the `build_ext` command, to retrieve the destination path
where the extension file was copied to.

Added
- Add the `gravelspoon` command to break out of the setuptools build isolation
and find the system NumPy includes.

Added
- Print error message stderr when re-raising assumed compilation error.

Added
- Print error message when re-raising assumed compilation error.