Travis: add automated build script
Travis: create real test environment, run tests with phpunit

Inspired by @icewind1991 and the Travis integration he wrote for his SMB
project, set up a virtual environment in which to compile and test this
library. Set up some basic tests and show the build result in the
README.
tests: do not include in release tarballs

Release tarballs contain the final shipping code only.

The tests are interesting for developers and the automated build system.
Outside of Travis, they won't run without determined effort to replicate
the test environment in Samba.