Implement support for turning .json files into Lua modules (#308)

* Stub implementation

* Flesh out feature and add tests. Other snapshots currently failing.

* Blacklist .meta.json in JSON handler

* Write to correct property (Source) instead of Value

* Update changelog

rojo-test/build-tests/json_as_lua/default.project.json

@@ -0,0 +1,6 @@
+{
+  "name": "json_as_lua",
+  "tree": {
+    "$path": "make-me-a-script.json"
+  }
+}