Convert docstrings to reStructuredText

This commit also includes:

  - whitespace / code formatting fixes
  - slight syntax related changes: except <exception_name>, e -> except <exception_name> as e
  - 3 pointless instructions instances have been rewritten [sorted] (spotted by semi-automatic check)

The unrelated changes shouldn't have any real impact on whipper's behaviour.

setup.py

@@ -13,6 +13,6 @@ setup(
     entry_points={
         'console_scripts': [
             'whipper = whipper.command.main:main'
-         ]
+        ]
     }
 )