Sphinx eager ".. only::" directive and other selective rendition extensions
Description
The implementation of ".. only::" directive in Sphinx documentation generation
tool is known to violate principles of least user surprise and user expectations
in general. Instead of excluding content early in the pipeline (preprocessor
style), Sphinx defers exclusion until output phase, and what's the worst,
various stages processing ignore "only" blocks and their exclusion status, so
they may leak unexpected information into ToC, indexes, etc.
This projects tries to rectify situation on users' side. It actually changes the
way Sphinx processes "only" directive, but does this without forking the
project, and instead is made as a standard Sphinx extension, which a user may
add to their documentation config. Unlike normal extensions, extensions provided
in this package monkey-patch Sphinx core to work in a way expected by users.
