Feature: Testing on travis

Made some unit tests and let them run against multiple PHP and ext-memcached versions as well as HHVM.

Tests are currently failing, but thats the matter from other issues, like:

https://github.com/LeaseWeb/LswMemcacheBundle/issues/32
https://github.com/LeaseWeb/LswMemcacheBundle/issues/25
https://github.com/LeaseWeb/LswMemcacheBundle/issues/21