Added CI to auto-build sphinx docs

This merge adds CI configuration to auto-build sphinx documentation for glue, mainly using sphinx-apidoc to render the package/module/function docstrings into HTML. The docs would eventually render to

https://docs.ligo.org/lscsoft/glue/

This should require little maintenance as long as the git tags are properly propagated, and the setup.py install_requires list is kept up-to-date.