deploy documentation to static sites

[shapiromatron]

Through trial and error, deploy pybmds documentation to two locations:

1. https://usepa.github.io/BMDS/. This shows documentation for the latest tagged (released) version and is appealing as it has the U.S. EPA GitHub subdomain as part of the URL. This is triggered automatically whenever a tag is applied to the git repository.
2. https://pybmds.readthedocs.io/. This shows documentation for current and prior tagged versions, so it may be useful for people working with older versions of the software. This capability is not available using the github.io subdomain without significant effort. This is triggered manually.

In addition, added assorted badges to home page of the GitHub readme for the BMDS repository, now that documentation is available.