Add travis and coveralls support.

I set up travis and coveralls for viennacl-dev. I did this to check if I could reproduce the test failure I reported in #105. But perhaps you're interested in incorporating these modifications upstream.

The basic idea is that an automatic build is fired off every time a change is pushed to github. This includes running the test suite. Test coverage data is collected as a side effect. An example of a test log is here:

https://travis-ci.org/d-meiser/viennacl-dev/builds/39989794

As you can see two tests are failing on the travis virtual machine. I have no idea why those tests are failing (they're passing on my local machine).