Add an adapter for postgreSQL

[ddluc]

It would be great if this ORM also worked with PostgreSQL databases. I wish I would have built it that way originally. Sigh.

It's going to be a relevantly decent undertaking but would be totally rad.

Good news is that all of the test cases (and really the top level implementation) are already laid out. We probably want to create an adapter class that abstracts out the individual DB libraries for mysql and postgresql respectively. Which is actually an interesting challenge.