Add Travis-CI support

I added support for using https://travis-ci.org

What is needed from you @warmcat :

1. Go to https://travis-ci.org
2. In the upper right corner click "Sign in with Github"
3. After you have logged in, click your name in the top corner and choose "Accounts"
4. Find libwebsockets in the list of repositories and turn it on.

After doing this, any push or pull request will trigger a new build on Travis, and you will get an e-mail if anything fails.

Example of what you get:
https://travis-ci.org/JoakimSoderberg/libwebsockets/builds/42092587

libwebsockets doesn't have any unit tests, but it has a lot of conditional compile flags. When adding new features it is not entierly uncommon to break some of these builds.

Ofcourse adding tests for the http://autobahn.ws/testsuite like I mentioned in another ticket would also re-verify that each commit doesn't break anything.

And also unit tests to validate isolated pieces of code (including valgrind check for instance).