added get_a_card method

get_a_card method added to Deck class; it grabs a random card from cards
added show_definition and show_answers methods to deck class
Merge pull request #4 from zachgersh/kelmers-branch

Kelmers branch
Merge pull request #3 from zachgersh/zach

Added infinite loop to get user input.
updated class flashcard. check parser method.
Fixed, merge conflict that was happening

Merge remote-tracking branch 'origin/wendy'

Conflicts:
	flashcard.rb
Started the logic to build a flashcard object.

Kelmer is going to finish this method I started writing.