Documentation Mungers

Basically this is like lint/gofmt for md docs.

It basically does the following:

iterate over all files in the given doc root.
for each file split it into a slice (mungeLines) of lines (mungeLine)
a mungeline has metadata about each line typically determined by a 'fast' regex.
- metadata contains things like 'is inside a preformatted block'
- contains a markdown header
- has a link to another file
- etc..
- if you have a really slow regex with a lot of backtracking you might want to write a fast one to limit how often you run the slow one.
each munger is then called in turn
- they are given the mungeLines
- they create an entirely new set of mungeLines with their modifications
- the new set is returned
the new set is then fed into the next munger.
in the end we might commit the end mungeLines to the file or not (--verify)