Working Version of Hangman problem

randomWord method:
   - asks user if would like to generate an adjective or a noun
   - uses the random-word gem to generate this random number

generateDashes method:
   - generates dashes depending on the length of the randomly generated word
   - these dashes used as spaceholders for user to guess the random word

addLetters method:
   - adds in the user's letter guess, if it is correct
   - updates what the user has correctly guessed so far

countLetter method:
  - counts the number of occurrences that a character has appeared in the word

hangman method:
  - uses all above methods to run the game
  - while loop quits if the user runs out of chances or if the random word matches
    what the user has guesssed