Respect txt2tags configuration
i.e.
Properly process Header Area (in pages)
Properly process Config Area (in pages)
Properly process ~/.txt2tagsrc (global config)

At the very least, there should be *some* way to make Wixi respect the
txt2tags '%! PostProc:' directive. This allows doing things
(particularly in (x)html) that can't be done any other way, like
embedding HTML tags which aren't already handled by txt2tags.

If this is already available, PLEASE document it, as I've tried
everything I can think of (including reading through the wixi sources)
to make Post Proc work, and I can't figure it out.

P.S. If I take the txt2tags formatted file from Wixi and run it
through Txt2tags.py on the command line, it works *exactly* as
expected.