Add support for php files with custom extensions

[jsobiecki]

It would be very helpfull to make possible to specify list of php files extensions (like for other tools, like ie phpcs). It will be helpfull for integration with custom frameworks, whose use slighty different php files suffixes names (*.install, *.module).

I prepared patch for PHP_CodeBrowser, that seems to work. I commited change to forked repository. More details here:
jsobiecki@d0ed50f