PHP CodeSniffer

Hello,

This adds support for the [PHP CodeSniffer](http://pear.php.net/package/PHP_CodeSniffer/) in SublimeLinter. Essentially this allows the linter to check code against different PHP coding standards. I tried keeping this functionality pretty flexible for different PHP standards and to allow people to customize it with a list of "ignore" rules.

To use:

1. [Install PHP Codesniffer](http://pear.php.net/package/PHP_CodeSniffer/)
2. Add any standards you may need (PEAR, Drupal, etc). The project comes with a number of standards, but some may need to be added.
3. In the SublimeLinter config you can add global options, see the main SubmlineLinter settings. You can also set project specific settings in a `.phpcsrc` file. This uses the same form as the `phpcs_options`.
4. Add `php => phpcs` (and maybe `html => phpcs`) to your `sublimelinter_syntax_map` option in the SublimeLinter config
5. Enjoy

Thank you for the great linter! This has been very helpful.