API v2

The whole point here is to support v1 at the same time as v2.  If we drop support for v1, we don't need this adapter at all.  This was just one way that I figured out how to maintain support for v1, but it doesn't matter to me which way it's done, so if this can be done a different way, that's fine with me.

Without this code, Grape receives /api/foobar, instead of just /foobar, or some such problem.  So this code just removes the extra piece from the route before passing it to Grape.