Add Travis continuous integration.

Depends on pull request #32 for the TestRunner.

Executes the TestRunner on each push and pull request on https://travis-ci.org/

For an example on my fork see: https://travis-ci.org/jbnicolai/MathBox.js
To enable this on unconed/MathBox.js see http://docs.travis-ci.com/user/getting-started/

In short:
- log in with your GitHub account on TravisCI
- allow access
- click the '+', find unconed/MathBox.js and flip the switch
- wait for a push to see an automatically triggered build