Reorganize help writing code.

Move all code related to printing the help (console or other formats)
into wman.cpp from pargs.c and filenm.c.  This allows making a lot of
functions internal to this file.

Move code related to markup substitution from wman.cpp into
helpwritercontext.cpp, making it a bit more C++-like in the process.

This commit is mostly cut&pasting code, but some small changes here and
there were required to make it compile (mostly, replacing direct access
to deffile[] with ftp2*() function calls).

Change-Id: I233be210f98c65ffc6308bc91021100bacf7c831