Move to PHP 5.3, namespaces and composer

Fixes #3 and beats some shape into the codebase.
Before merging you should tag the current release and add a note about just pull-updating will break things.
Use `composer install --dev` to get phpunit version and run `vendor/bin/phpunit test` to run tests.

Adding the package to packagist, and running tests on travis should be a no-brainer as next steps.