Adds Travis-CI testing

This commit adds Travis-CI testing, which allows
free and easy continuous integration for pull requests
and new commits. It also adds a `make deps` target
in the Makefile for easily adding the dependencies.

It can be enabled here:
http://docs.travis-ci.com/user/getting-started/#Step-one%3A-Sign-in

Just follow instructions 1-2, three is already done. Thanks.