check-manifest

As suggested by https://github.com/jayvdb run manifest checker and oops,
it finds that we forgot to include pyproject.toml for testprog/golang_pyx_user:

    missing from sdist:
      golang/pyx/testprog/golang_pyx_user/pyproject.toml
    suggested MANIFEST.in rules:
      recursive-include golang *.toml

-> Fix MANIFEST.in in generic way to include golang/*/*.toml

The bug was not affecting pygolang usage - only golang.pyx.build tests were
failing for sdist installed pygolang.

MANIFEST.in

 include COPYING README.rst CHANGELOG.rst tox.ini pyproject.toml
 include golang/libgolang.h
 include golang/runtime/libgolang.cpp
-recursive-include golang    *.py *.pxd *.pyx
+recursive-include golang    *.py *.pxd *.pyx *.toml
 recursive-include gpython   *.py
 recursive-include 3rdparty  *.h