Critic Markup filter

[Dirk Laurie <dirk.laurie@...>]

CriticMarkup <http://criticmarkup.com> is a way to indicate in a text
document which deletions and insertions are to be applied. It can be
converted to a printable document in three ways: keep markup
instructions in the text, rendering them by some typographic
convention (overstriking, underlining etc); respect insertions but
remove all other markups; restore deletions but remove all other
markups.

The very sparse symtax is intuitive and easily learnt.

I {--guess hopefully--}{++estimate++} that implementing a Lua filter
for this won't take me longer than a couple of hours (having lpeg
available, I hasten to add). Still, if someone else has done it, why
reinvent the wheel?

So put up your hand, complete with URL to your preferebly GIT'ed code,
and I shall desist.