Finish implementing basic spec

[sandersky]

Currently we are not implement the full JSON spec for the basic types

To-do

• Add missing object validation
• Improve documentation to mention importing Flow types
• Add $ref support
• Add ability to provide list of valid formats for string so we can flag any typos (maybe an optional second argument on the string method?).
• Support type that is array of strings? I'm not sure if this is useful other than if we maybe convert things like:

  {"anyOf": [{"type": "number"}, {"type": "string"}]}

  to

  {"type": ["number", "string"]}

  so the output is minimal (this could even be a completely separate utility called minify, whose sole purpose is to make these small optimizations.
• Make sure enums are fully supported
• Support media
• Support sub-schemas
• Support $schema and make sure validation is applied accordingly
• Allow validating a value against a given schema