Add DEVEL_QUICKCOVER_{INCLUDE,EXCLUDE} filters

[JRaspass]

At $work we use these environment variables to massively speedup coverage by only dumping coverage for files we care about. We set DEVEL_QUICKCOVER_INCLUDE to the path to our code, and then use DEVEL_QUICKCOVER_EXCLUDE to exclude templates, testing libraries, etc.

There's almost certainly a better way to write this, and it really needs docs, but I'm just putting this out here to start a discussion on whether something like this should be merged. We've been using this successfully to speedup our CI tests for about half a year now.

[gonzus]

This looked good to me: useful and to the point. So I just went ahead and merged it. Thanks!