Move testing to travis

Spoke to Ollie a while ago about this, and said I'd do it, so now it's done.

Makes sense since it's open source and is useful to test against different PHP versions; starting at 5.3 because composer is only 5.3.2+ and we basically depend on it. Minor downside is that test pass/fails aren't reported in hipchat, in order to do this we'd need to switch this repo over the HC/GH integration no one much likes. Might be ok for one repo, perhaps?

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