Refactoring: Path API compatibility with pathlib

Refactored dupeGuru to make hscommon.path's API a bit close to pathlib's
API. It's not 100% compatible yet, but it's much better than before.

This is more of a hscommon refactoring than a dupeguru one, but since
duepGuru is the main user of Path, it was the driver behind the
refactoring.

This refactoring also see the introduction of @pathify, which ensure
Path arguments. Previously, we were often unsure of whether the caller
of a function was passing a Path or a str. This problem is now solved
and this allows us to remove hscommon.io, an ill-conceived attempt to
solve that same ambiguity problem.

Fixes #235.

core/gui/directory_tree.py

@@ -31,7 +31,7 @@ class DirectoryNode(Node):
         self.clear()
         subpaths = self._tree.app.directories.get_subfolders(self._directory_path)
         for path in subpaths:
-            self.append(DirectoryNode(self._tree, path, path[-1]))
+            self.append(DirectoryNode(self._tree, path, path.name))
         self._loaded = True
     
     def update_all_states(self):