- add a IOException and a main filesystem exception interface
- whenever an action fails, an IOException is thrown
- add access to the second and third arguments of touch() function
- add a recursive option for chmod()
- add a chown() method
- add a chgrp() method
- Switch the 'unlink' global function in Filesystem::symlink to Filesystem::remove.
BC break: mkdir() function now throws exception in case of failure instead of returning Boolean value.
