Aiopg

[hsz1273327]

postgresql suport,uri parser,database factory function with unit tests

[kszucs]

First of all, thanks for the PR!

I hope You don't mind, but I'd like to request a couple of changes:

• don't rename the tests directory to test
• drop the error and util files, these are not present in original peewee distribution, i don't intend to introduce new abstractions
• peewee already has a db uri parser in playhouse extension: https://github.com/coleifer/peewee/blob/master/playhouse/db_url.py
• keep using pytest framework instead of unittest

Just narrow the scope of this pull request to add aiopg adapter.