19 parse json requests

[xentek]

• Adds new middleware ParseJSONBody that will parse the request body adds all key/value pairs it finds to the rack env, as if it was sent as form data.
  • It requires that the request contain a Content-Type header that ends in json for it to kick in
• If the json can't be parsed, a 400 error will be returned (via new JSONParseError class)
• The middleware will run before SanitizeParams so that we can properly enforce business rules as defined on the resource
• If any query string values exist that use the same key as one of the params parsed, the json value should win out.

refs #19