Adds a reasonably feature complete implementation of full text search
using the built in PostgreSQL engine. It uses public APIs from
Expression and Lookup.
With thanks to Tim Graham, Simon Charettes, Josh Smeaton, Mikey Ariel
and many others for their advice and review. Particular thanks also go
to the supporters of the contrib.postgres kickstarter.
Stefano Chiodino
Mads Jensen
chillaranand
Claude Paroz
Marc Tamlyn