Using a g2-style "chained update hook" as a VREF doesn't *quite* work:
- all STDOUT from the hook is lost
- worse, all lines get parsed as a ref followed by a message, and if
the ref doesn't look like a ref it dies
So now we do all this only if the message starts with 'VREF/'. Any
other output is just printed out as is.
- explicit 'list' gives way to mindmap, ...
- 'fm2mt.pl' to produce master-toc.mkd from the mindmap
- mkdoc no longer ignores master-toc.mkd, calls fm2mt.pl itself
and LOTS of changes to the actual docs
