Set up Travis CI

Broke up the monolithic shell script into separate steps so the output is
clearer when it fails. These scripts are just thrown into a gist for now at
https://gist.github.com/jasonmp85/9963879. I had to enhance them to allow a
`PG_PRELOAD` environment variable to inform Travis what libs should be
preloaded (i.e. if the extension being tested has hooks).