New features

• Added calendar button to go back and play historical puzzles. Completed puzzles are tracked to let you know which ones you have solved.
• The keyboard will show word-specific clues based on the currently selected word.
• The middle letter is now treated as a separate clue in each word.
• Orange clues if a matched letter is not in the current word are on by default. See the help screen for more information. Turn on hard mode to disable.
• Gives you the answer after 10 failed guesses.