Prep for alpha release

[frreiss]

This PR includes changes to prepare for an alpha release. I have been using the source branch for this PR to test release tooling. Current release testing results:

• Github pages web site: https://frreiss.github.io/tep-fred/
• Github repo page: https://github.com/frreiss/tep-fred/tree/branch-alpha
• Package: https://test.pypi.org/project/text-extensions-for-pandas/0.1a4/

Main changes in this PR:

• Created a (stub) web site for Github pages under docs (Github pages requires the web site to be either at the root of the repo or in a subdirectory called docs)
• Moved the API docs that used to be at docs to api_docs
• Fixed some minor problems with project metadata
• Rewrote most of README.md
• Created a readme for the PyPI page: package.md

[frreiss]

Merging these changes to master as soon as CI finishes.