Create the "Minimal" card

This is the most basic card that can be defined. It has nothing special, and is
mostly used to test the default arguments of the Card class. See
test/test_card.rb for it's usage.
A couple more tests for library

- Don't add a card that failed some validity check
- Do throw an error when we can't find a specific card
Make sure to empty the library before running tests
REALLY basic tests for a Rule card