Test and document support for built-in data types

[jmealo]

I started some work on doing this within Lapidus, but I think it should be a part of the tests for decoding-json.
https://github.com/JarvusInnovations/lapidus/blob/master/test/postgresql.test.js#L127

If this helps, here's a JSON structure with the data types:
https://gist.github.com/jmealo/d7a75257d4c12f79aa2c

This is the jQuery snippet for the Chrome console that I used to generate the JSON right from the documentation:
https://gist.github.com/jmealo/d1ae63bc61976af80b50

If it helps, I can probably contribute the SQL to create a test table along with INSERTs and expected output. I'm not sure if row_to_json could be handy in comparing expected output and behavior.

We should also decide (and perhaps provide a configuration option) if big numbers should wrap or be sent as a string.