Read-structure-step

* Updated the README file to give a better description.

* Updated the short description in setup.py to work with the new installer.

* Added keywords for better searchability.

Updated for compatibility with the new system classes in MolSystem
2021.2.2 release.

Internal: switching CI from TravisCI to GitHub Actions, and in the
process moving documentation from ReadTheDocs to GitHub Pages where
it is consolidated with the main SEAMM documentation.

Removed leftover debug print statements.

* General bug fixing and code cleanup.

* Part of release of all modules.

First release on PyPI.