simplify JSONValue

[swhitty]

Simplifies public interface of JSONValue removing redundant methods.

renames JSONValuePattern to JSONBodyPattern as it is a HTTPBodyPattern implementation.

adds == operator for common comparisons to JSONValue

JSONValue.string("fish") == "fish"
JSONValue.number(10) == 10
JSONValue.bool(true) == true

allows for routes to use:

 let route = HTTPRoute(
   "POST /fish",
   jsonBody: { try $0.getValue(for: "$.food") == "chips" }
)