gfx bugfixes
Adding a pretty cool string macro to utility.h

Makes handling sets of static strings supereasy.
Fixing coord orders
Added full-featured json module, on top of jsmn

A `struct json_doc` keeps the source characters, and the data needed for
jsmn (see http://zserge.com/jsmn.html).

Then a `struct json_ref` is used to read through the json document. The
json_ref can get the key string and the value. You can call either
json_next to advance an existing json_ref, or you can call
json_childref, which returns a new json_ref to the first child object of
the json node that json_ref refers to.

A rough example is in gameplay.c:init_data, which opens the json_doc,
finds the object named "player", then uses RL_Object_SrcJSON with the
json_ref to that object. RL_Object_SrcJSON() walks through the child
object the same way that init_data walked through the root object, and
fills in the player object with information sourced from the json
document.