Added postgresql.

Added user and database creation to bootstrap.sh. Checks if user and database already exists.
Pull SQL logic into a separate file.

Running the Vagrantfile more than once will cause an error message since the database would already be created. This doesn't cause any problems though.
Merge pull request #14 from natebrennand/master

add spec and link to spec in README
Merge pull request #17 from davidhao3300/add-postgresql

Added postgresql.