Python mapping with new 9.2 data types

Hello,

I've worked at Python-Postgres mapping for the new PostgreSQL 9.2 data
types. They should be released with the next psycopg2 version.

The current design, susceptible to changes if needed, is documented here:

- JSON adaptation: http://initd.org/psycopg/docs/extras.html#json-adaptation
- Range data types: http://initd.org/psycopg/docs/extras.html#range-data-types

The code is available in feature branches of my github repository:
https://github.com/dvarrazzo/psycopg

Any feedback (tests, comments, docs corrections) is very welcome.

Regards,

-- Daniele