Add support for partial path match in the skip option

[ccojocar]

This is a fix for issue #124. The skip option is extended to support partial path match. Currently it is possible to exclude the vendor folder with this pattern only:

gas -skip "*vendor*" ./..

I extended the fileList to support also partial paths like this:

gas -skip vendor ./..

[gcmurphy]

Getting the skip / inclusions lists right has been a bit of a nightmare. This looks like a sensible change