Fixed test_oauth; Board.get_cards accepts a dictionary of filters; Code reformatting; README update

Sorry for the huge diff. All of the whitespace changes took place in that first commit, so viewing the changes since that one might be more helpful.

Whitespace changes were made because there were only two files and the tabs were bugging me. Here is the relevant PEP-8 - http://www.python.org/dev/peps/pep-0008/#tabs-or-spaces

There is also a breaking change in that I changed the order of the arguments in the TrelloClient constructor because it felt really weird alternating between the Trello API Key and the Trello OAuth Token. Especially because you might have an API Key but not an OAuth Token (but you will never have an OAuth Token and not an API Key), in which case your constructor arguments might look like 
    TrelloClient('my-api-key', None, 'my-api-secret', None)

With the changes, you can just omit those last two arguments if you don't have an OAuth Token.