Auto-check compiled file was updated

Right now it's easy to change original matcher classes but forget to run `php generator/run.php` script to regenerate `Hamcrest.php` file with global functions.

Proposing to add a build step, that for each PR would attempt to regenerate `Hamcrest.php` file and if some changes were made, then fail the build.

This way a contributor will know that he needs to include a generated file in PR as well.