Update development dependencies and move doc-specific ones out.
Review Request #9833 — Created March 26, 2018 and submitted
This updates the required versions of kgb, Sphinx, and beanbag-docutils
to the latest versions.
Along with this, it moves the doc-related dependencies into
doc-requirements.txt, so they're not needed for building the source
tree. This helps with build issues on Python 2.6 and just lowers the
requirements overall for working on the source tree.
Successfully installed both the development and doc dependencies.
Unit tests pass (except for two that are broken upstream).