templatefilters: wrap all filters in dedicated functions This will highly simplify the docstring integration. I measured "hg log --style=changelog" duration on mercurial itself and could not detect any difference.

  $ echo '[Section]' >> $HGRCPATH
  $ echo 'KeY = Case Sensitive' >> $HGRCPATH
  $ echo 'key = lower case' >> $HGRCPATH

  $ hg showconfig Section
  Section.KeY=Case Sensitive
  Section.key=lower case