Enable Travis CI-Builds

[philipp-classen]

Hi Greg,

I added a Travis configuration (.travis.yml), so we have continuous integration. It verifies that the code builds and the tests pass (there are not many yet). The compilers are currently g++ 4.9 and clang 3.7.

From my understanding, only the owner of the project can enable the Travis. This URL should bring you to the Travis configuration:
https://travis-ci.org/grogers0/CppQuickCheck/

For testing, I enabled it on my forked project:
https://travis-ci.org/philipp-classen/CppQuickCheck

Would be great if you can enable it on the main project, too.

Thanks
Philipp