Use real globbing when defining ClassSet

I have test code that lives alongside my production code, in "Tests" sub-directories that I would like to exclude.

It does not appear possible to use real glob syntax "**" to mean "any directory". E.g.

```
$classSet = ClassSet::fromDir(__DIR__.'/src')
    ->excludePath(__DIR__.'/src/**/Tests/')
;
```

This does not work and the test files are being included in the analysis.

Thanks!
