Advanced JSON Schema support

[jgaehring]

There's a lot more that can be done to support JSON Schema evaluation, but I just want to draw attention of a couple potential features I brought up in #25 (comment), before I close that issue:

• provide validation, via AJV
• use AJV's type definitions

I have no time-frame for either of these, but they would make a nice addition.

[duarteoctavio]

I believe a lot of the work I've done here can be merged into Farmos.js to get that functionality to work.