Update datapackage.json to latest specifications

[danfowler]

http://specs.frictionlessdata.io/

• Move enum and required fields to within constraints object
• Transform license field (string) to licenses field (array)
• Update schema reference ("cmoa-schema") to JSON Pointer (current tools don't support atm but will soon)

[workergnome]

Modified the file to accommodate the first two—let me know when tool support is ready for the last.

[danfowler]

@workergnome OK, will do! 👍