First more-or-less working version: does terms, booleans, qualifiers

First more-or-less working version: does terms, booleans, qualifiers
and relations.  Doesn't do multi-char relations (<= etc., "all" etc.),
proximity,
Quoting for XML not yet done.
Rendering tree back down to CQL is incomplete/untested.
Class documentation is all but non-existant.