Add parser for OGC Filter version 1.0 and 1.1

Adds a parser for OGC Filter Encoding version 1.0.0 and 1.1.0. The parser
supports read and write.

This is not yet ready for review since it depends on the javascript filter language that @tschaub is working on, this will need to be integrated later, but I thought I'd put this out here already.