fix rspec to output human readable messages with `rspec -f d`
fix number card range that should be 2..10 but 1..9.
add InvalidCardError and its spec.
add alternative_value for ace.
change to use described_class instead of BlackJack::Card in spec.
rename black_jack to blackjack, BlackJack to Blackjack like spelling on Wikipedia.
add Player with name attribute.
add Blackjack::Dealer and its #name spec.