remove references to pythonhosted.org (issue #293) The pythonhosted service is no longer supported. Update links to point to docs.kallithea-scm.org (which redirects to kallithea.readthedocs.io) While at it, fix the whoosh pythonhosted.org reference as well.

# 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
.