Check only PHP files by default, include JS and CSS optionally

[dingo-d]

Currently the sniff process can fail due to memory exhaustion when the sniffer comes across the minified JS file.

Currently, there is an option to check only PHP files. This option should work in reverse - if checked, JS files would be included in check (with a note that the sniff process may fail).

This would help with the current issues some authors and reviewers are experiencing.