Merge branch 'take-2'

The take-2 branch started over with a new grammar based directly on
the grammar from the C99 specification. It doesn't try to capture
things like balanced sets of parentheses for macro arguments in the
grammar. Instead, it merely captures things as token lists and then
performs operations like parsing arguments and expanding macros on
those lists.

We merge it here since it's currently behaving better, (passing the
entire test suite). But the code base has proven quite fragile
really. Several of the recently added test cases required additional
special cases in the take-2 branch while working trivially on master.

So this merge point may be useful in the future, since we might have a
cleaner code base by coming back to the state before this merge and
fixing it, rather than accepting all the fragile
imperative/list-munging code from the take-2 branch.