caching: invalidate Repository cache of README and RSS based on latest revision hash in its .changeset_cache Avoid using the the more heavy and complex CacheInvalidation. Note that raw_id only is passed to the getter function as cache key, in order to make sure new data is retrieved whenever the repo changes.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.