Some early work on varous query objects.
Merge branch 'develop' into feature/query_parser
Work more on query tree structure.
More work on query tree structure.
More work.
Merge branch 'feature/parser' into feature/query_parser
More work on query parsing.
Literal parsing; term parsing hooks; unit test stubs.
More debug stuff.
Parsing dates should work.
Fix a typo.
Symbol parsing works.
Finish parsing for languages.
More complete and descriptive error messages.
Construct full trees; support inverting with not:<term>.
Change UnaryOp.NOT to work with BinaryOp.{OR,AND}
code
Clean up SPLIT_QUERY_STRING.
Finish _scan_query(), _split_query().
Begin work on a model for boolean logic parsing.