Ensuring root path is respected in all drivers.

Flysystem will now resolve relative paths, when unresolvable it will throw an exception (LogicException). file (or dir) paths that reach outside of the specified root are now disallowed which makes the entire API more secure and friendly to use. A path like some/nested/../location will be converted to some/location, making sure the cached metadata is correct and protecting you from possible security exploits when building file managers.