Augmented the JSONMaster API

[ppasupat]

• "q" command now takes a map with keys "utterance", "context", and "fields"
• More documentation

[sidaw]

new API looks good. It might make sense for fields to be a key in context instead of top level

• we also want it in the accept and context commands
• parsing needs to be aware of fields, so eventually it has to go into a ContextValue. The alternatives are extending Example, or let the client tag the utterance. It seems to me that putting more stuff into ContextValue is the best of the 3. Just a heads up, let me know if you have opinions on this.