Ignore all dot leading folders

[gforcada]

@reinout indeed, ignoring all dot leading folders is important!!

I forgot to do some real testing, and once I did that, after the release, the first one already showed the problem: .tox stalls the processing 😕

I refactored, a bit, the scanners to share the filtering logic on a single function 🧹

[coveralls]

coverage: 99.968%. remained the same
when pulling 08b2c38 on ignore-tox
into 78e8937 on master.

[gforcada]

We might want to expand this by allowing users to specify a list of folders to be ignored, probably.

node_modules is the default folder if you have some JS code within a python distribution, but the name might as well be another...

[gforcada]

I did merge and release z3c.dependencychecker==2.14.1 to fix this obvious performance regression 😓

[reinout]

Common problem. .gitignore, .dockerignore... There are multiple places where I occasionally trip over to-ignore or to-include stuff. I wonder if there's some existing thing we can use? Probably we'll need a custom one.

[gforcada]

Another approach would be to use something like git ls-files and only scan those files...