templatekw: port implementation of showparents() from changeset_templater
It isn't cool, but we can peek at ui flag via repo.ui. So, it is possible
to implement showparents() in templatekw, and therefore we can eliminate the
dockeywords hack.
.. Common link and substitution definitions.
.. |hg(1)| replace:: **hg**\ (1)
.. _hg(1): hg.1.html
.. |hgrc(5)| replace:: **hgrc**\ (5)
.. _hgrc(5): hgrc.5.html
.. |hgignore(5)| replace:: **hgignore**\ (5)
.. _hgignore(5): hgignore.5.html