WEIgnore : Allow comments on the file

To be able to generate a useful and self-explained <code>.weignore</code> file with [side-waffle]() as requested on ligershark/side-waffle#145 and to be compliant with the [.gitignore documentation](http://git-scm.com/docs/gitignore) even if [jshint doesn't handle it yet](https://github.com/jshint/jshint/issues/1757) we need to handle correctly comments on that file.