FileFilterExclude / FileFilterInclude

Hi folks,

I needed a functionality to filter a set of files (FilePathCollection) given by an array of wildcard path strings, e.g:

```
string[] filter= new string[] {
@"**/*.gif",
@"**/*.jpg",
@"**/*.png"
};
```
Specifically I needed the possibility to get all the files that match the filter criteria (IncludeFiles) and on the opposite to get all the files that do NOT match the filter criteria (ExcludeFiles).

Unfortunately I'm not familiar with pull requests - but if any one is interested feel free to include the attached methods in this library!

[FileFilter.txt](https://github.com/cake-contrib/Cake.FileHelpers/files/2230620/FileFilter.txt)