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_me/fs.py

@@ -36,7 +36,7 @@ class MusicFile(fs.File):
     def can_handle(cls, path):
         if not fs.File.can_handle(path):
             return False
-        return get_file_ext(path[-1]) in auto.EXT2CLASS
+        return get_file_ext(path.name) in auto.EXT2CLASS
     
     def get_display_info(self, group, delta):
         size = self.size