Added deck_deleteDeck().
Added the declaration and the documentation for deck_deleteDeck().
Added a new error, DECK_NULL.
Modified all the file.
Added the tests for deck_deleteDeck().
Released the memory from deck_createDeck().
Fixed releasing of the memory from test_deck_createCard() and test_deck_createDeck().
Merge pull request #14 from EnachescuAlin/deleteDeck

Delete deck