spurious return
Adding hstore support.  map[string]string will encode to hstores and throw errors on hstores with NULL values, and there is now a NullHstore type that is basically map[string]NullString and will both accept and decode NULL values properly
Instead of native map[string]string, use type pgx.Hstore instead
Merge pull request #36 from anaxagoras/custom-types

Hstore support via map[string]string as well as NullHstore, which amounts to {Valid bool, Store map[string]NullString}