Add support for CraftQl

[keithmancuso]

Currently working on a site using marks amazing GraphQl Plugin and right now your fields are the only thing I had to resort to boring old rest for.

He has pretty specific instructions on how to add support for third party field types that seems pretty straightforward. Would love to see this as an option, especially for the embed fieldtype

[leevigraham]

I'm happy to accept a PR for this, otherwise I'll try and add it this week.