templatekw: add {path} keyword to host documentation
It's hidden since I'm not sure if filectx templates can be a thing. The plan
is to add {status}, {size}, etc., which are usable within {files % ...}
context.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.