Automate tests

[sirbrillig]

The tests should be able to run with a simple call to composer test.

[GaryJones]

It would be good to get some instructions written up as well, even if the tests are ultimately then available via composer test.

I started to put together something to run the tests, but seemed to be going down a rabbit hole that may not have been necessary. I guess you'd been running tests already, but I hadn't figured out how you were doing that.

Do be aware though, that it should cater for PHPUnit and PHPCS NOT being available globally - i.e. they should be require-dev dependencies, and any paths to them reference vendor/bin/php* instead of global installs.

Tieing this all into a Travis CI webhook would be the obvious next step afterwards.

[sirbrillig]

Now the tests can be run with composer test. I made #15 to cover adding CI.