Add note on client encoding to the quickstart page
Added info about mailing list
Add support for two-phase commit DBAPI extension

Thanks to Mariano Reingart's TPC code on the Google Code version:

https://code.google.com/p/pg8000/source/detail?r=c8609701b348b1812c418e2c77bb1ec272e6f29c

on which the code for this commit is based.
Prepare for new release