Parse json body payload in webhook handler
Parse json body payload in webhook handler

Unfortunately Scotty serves a 500 "internal server error" when parsing
fails, though it should serve a 400 "bad request". I tried for a while
to make it respond with 400 if parsing fails, but this is not so easy,
so let's not bother for now. This is a quick prototype after all.

ruuda/hoff,ruuda/hoff