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.

hscommon/desktop.py

@@ -7,6 +7,7 @@
 # http://www.hardcoded.net/licenses/bsd_license
 
 import os.path as op
+import logging
 
 class SpecialFolder:
     AppData = 1
@@ -38,7 +39,13 @@ def special_folder_path(special_folder, appname=None):
     return _special_folder_path(special_folder, appname)
 
 try:
-    from cocoa import proxy
+    # Normally, we would simply do "from cocoa import proxy", but due to a bug in pytest (currently
+    # at v2.4.2), our test suite is broken when we do that. This below is a workaround until that
+    # bug is fixed.
+    import cocoa
+    if not hasattr(cocoa, 'proxy'):
+        raise ImportError()
+    proxy = cocoa.proxy
     _open_url = proxy.openURL_
     _open_path = proxy.openPath_
     _reveal_path = proxy.revealPath_
@@ -71,4 +78,14 @@ except ImportError:
             return str(QDesktopServices.storageLocation(qtfolder))
         
     except ImportError:
-        raise Exception("Can't setup desktop functions!")
+        # We're either running tests, and these functions don't matter much or we're in a really
+        # weird situation. Let's just have dummy fallbacks.
+        logging.warning("Can't setup desktop functions!")
+        def _open_path(path):
+            pass
+        
+        def _reveal_path(path):
+            pass
+        
+        def _special_folder_path(special_folder, appname=None):
+            return '/tmp'