scm: refactor install_git_hooks Rename, simplify, and negate some logic to make the flow more readable to me and give better logging. For example, "force_create" were more about "force overwrite". Calling it "force" is more precise.

# 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
.