0.9.0 released

changes

1. Changed the dialect from psycopg2 to pypostgres. This should be
   mostly backwards compatible, but if you notice weird issues, this is why.
2. You can now plug-in your own dialect using pg.init(..., dialect=my_dialect),
   or setting the dialect on the pool. See the top of the connection file
   for an example of creating a dialect. Please let me know if the change from
   psycopg2 to pypostgres broke you. If this happens enough,
   I might make psycopg2 the default.