Handle reading rdf data from files. Use underscores for uid and xid, keeping it in sync with internal usage. Output uids as hex.

Make list matrix work, yeah! This would serialize uids for the next query, which would then again return a matrix, so on and so forth.

BREAKING change: convert to JSON. Given we're not tracking uids for each query uid, this will cause problems for the result. So, have to re-structure stuff here.