updated search/select queries for json.pl

[avuserow]

search/select should:

accept arbitrary numbers of key/value pairs for searching metadata (currently artist, album, title, track, length). Multiple values for the same tag are treated as OR (since AND is a bit weird). Multiple keys are treated as AND (so you can specify artist and album). We can also support operators for numeric columns so we can do 'length<' for searching length less than a certain song length.

accept limit and offset, so clients can sanely paginate the responses. The default limit will be some nice high number like 1000 or 5000.