Loop until user quits
Refactor menu options and add prompt for checkout
Library and CheckoutBookOption list books with numbers
Checkout book functionality added. Refactored and added Console class for taking user input.
Moved printing welcome message to Console
Added success message for successful checkout
Failed checkout message printing but not re-asking for input.
Finished returning books. Refactored: injecting menu options in main, adding tests for menu options from application.
Merging upstream
Merge remote-tracking branch 'upstream/master'

Conflicts:
	test/com/thoughtworks/biblioteca/ApplicationTest.java
	test/com/thoughtworks/biblioteca/BookTest.java
	test/com/thoughtworks/biblioteca/LibraryTest.java