config: refactor beaker configuration While refactoring: * drop support for 'cache.' prefix - it is only 'beaker.config.' that ever has been documented or used in examples * make prefix stripping more safe (if the prefix should appear twice in the key) * trust exactly what has been configured - drop stripping of strings * drop int conversion of 'expire' - beaker documentation suggests strings are fine

# 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
.