Cleaned up some code

-deleted old authorize-url function
-let the user pass in options when they authorize-client
 like the name and expiration rather than hard coding it.
 If they don't pass any of these in it will use defaults
-optimized trello-get to use get-url
Updated test-suite to reflect the new oauth functions
updated core and tests to use :pre and :post conditions to save a buttload of code.

-instead of attching :errors onto a card now they library will throws an assertion error if the user tries to pass in data that doesn't fit what's required which makes much more sense