Update docs to use more recent sphinx blueprint

[ijnek]

Updates the docs to use a more recent sphinx blueprint, since the current one is 9 years old.

• removes the version evaluation done in conf.py. I think this isn't needed since RTD can figure this out using the git tags in the repo.
• Adds sphinx-rtd-theme to requirements.txt, rather than using logic to figure out if we're on RTD or not. Maybe we could add instructions to install the reuiqrements.txt for anyone working on the docs, to the root README.rst.
• Gets rid of /home/user/bloom/docs/glossary.rst: WARNING: document isn't included in any toctree, by commenting out html_static_path in conf.py
• Extracts the general description of bloom out of index.rst into bloom.rst, so it displays in the sidebar table of contents correctly.

[ijnek]

Gentle ping.

[ijnek]

@nuclearsandwich Would you be able to give thoughts on this when you find some time? Thanks!