Filtering data is not sufficiently flexible

[msarahan]

• Multiple conditions need to be additive (in all of Boolean logic glory).
• need expression as some reasonable human readable string (or otherwise, a way to name models, since models specify this string to reconstruct the filter to the corpus.)

Approaches:

• Conform to ES existing syntax (JSON)
• hairy eval/exec with string formatting (might be a necessary implementation detail for DictionaryCorpus)
• Anything else?

[msarahan]

May be useful to use pyparsing: https://gist.github.com/thomasst/5520204