Next step adapting parmesan-heads.mf to mf2pt1.

Next step adapting parmesan-heads.mf to mf2pt1.

Noteworthy changes:

. New macro `get_subpath' which returns a subpath in the same direction as
  the curve.  Update callers to use it.

. Split punctum_char into three macros (punctum_char, plica_char, and
  epiphonus_char), simplify them and fix outlines.