Ignore matchers run against absolute paths

[conartist6]

This makes it impossible to, make an ignore entry like path/in/my/project.

[conartist6]

Also the code goes to the trouble of creating a reusable matcher, but it only ever uses that matcher once. Creation of the matcher can and should be pushed up a line, out of (path, stats) callback for perf.

[conartist6]

And finally, if you pass a function as the ignore expression, a promise is not returned from the expression, leading to crashes. I certainly expected to be able to pass an ignore function, instead of having to pass an array of ignore functions.

[conartist6]

I'll make a PR if I get around to it. For now I'm able to work around these issues