Finally moving to official org.json implementation!

[carterpage]

Fix for issue #179.

This is a fundamental change and will require a major version increment (2.0.0) at the next release.

Replace org.json dependency to use the org.json package.

Some behavioral changes / possible gotchas:

• Duplicate keys are no longer supported, which is consistent with expected behavior.
• JSONException is now a RuntimeException and does not need to be declared as thrown.
• JSONArray.put cannot simply accept "null" as a value and requires casting or JSONObject.Null