Postgresql support

I believe PostgreSQL is increasingly a more popular database than MySQL, and for our purposes I believe it would be useful to support PostgreSQL.

I suspect long term we want to abstract away from specific DB implementations and use an ORM, but for now, continuing with your approach, I believe this is manageable.  

I had to upgrade the MySQL driver as I found downloading the `master` branch of your repo would not run locally because of date conflicts and null columns.