Convert docstrings to reStructuredText

[JoeLametta]

WIP and untested. For more information please see #9, #73.
Unrelated changes included in this branch (made after a new PEP8 cleanup stage):

• Whitespace / code formatting
• Syntax related: except <exception_name>, e -> except <exception_name> as e
• Pointless instructions (see the following block). Spotted by semi-automatic conversion (only 3 instances)

# OLD
var = self.var.keys() = sorted(self.var.keys())
var.sort()

# NEW
var = sorted(self.var.keys()) 

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