Search expression parsing library

[isoos]

Search expressions on the pub site are a bit ad-hoc, and their parsing is will get more and more complex as new requests come in. We'll need a formalized query format with a (separate) query library that does the parsing and exposes the query structure.

This should include:

• grouping expressions: AND, OR, with ( ... ) sub-groups
• field:value expressions
• "exact match phrases"
• (optionally) weights