Support JSON schema

[loleg]

Ability to validate a JSON document according to a JSON Schema definition, as per http://json-schema.org/ - Implementation could look like Python's jsonschema

[loleg]

By the way, I did check JSON2.jl and JsonBuilder.jl for this capability and came up short.

[odow]

Leaving this link for posterity: https://github.com/fredo-dedup/JSONSchema.jl.

Alternatively, this issue can be closed. I don't think it is a job for JSON.jl.