- Made isPrimitive public, as it is vastly useful (returns true for the 8 primitives or their primitive wrappers)
- Fixed place where String was written out as {"@type":"string","value":"abc"}.  Strings should always be written natively in JSON, now that json-io is not allowing references to them (no @id, no @type fields for Strings).  The JsonReader was already consolidating many well known Strings ("true", "false", etc.)