Add a library with filesystem-related utilities for grunt

The library offers these functions:
- `mkdirRecursiveSync` To create a directory and its ancestors
- `escapeShellArg` To escape parameters passed to shell commands
- `directoryParser` To allow easy processing of files and directories (for an example see https://github.com/mlocati/concrete5/blob/grunt-remove-short-tags/build/tasks/remove_short_tags.js#L23-L51)