Adds a postgres logger.

Simple class that can be subclassed in place of SimpleExperiment to log to a postgres database.

Talked a little about it here: http://blog.trenthauck.com/posts/pelican-plus-planout/
Is there a safer way to do this? This code just makes me think of:

![](http://imgs.xkcd.com/comics/exploits_of_a_mom.png)