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/tests/base.py

@@ -102,11 +102,11 @@ class NamedObject:
     
     @property
     def path(self):
-        return self._folder + self.name
+        return self._folder[self.name]
     
     @property
     def folder_path(self):
-        return self.path[:-1]
+        return self.path.parent()
     
     @property
     def extension(self):