Scalatra + swagger

Makes it easy to integrate Sumac args with Scalatra, and get swagger docs from the Sumac definitions.

Everything isn't supported yet, but its a decent start -- primitives, `DateTime`, and collections of those.  It actually wouldn't be too hard to generate swagger docs directly from sumac, and skip scalatra completely (eg., if you want to use w/ unfiltered).
for a long time I've resisted making `@Required` have special status, I wanted it to be "just another validation" -- but this makes it special.

perhaps I really should go the other route, and let each annotation adjust the swagger docs.  (Eg., `@Range` should be reflected in swagger docs also.)