Rewrote xkcd_password in Node.js, uses local file

- The word dictionary is
  http://scrapmaker.com/data/wordlists/twelve-dicts/2of12.txt
- For more information, see
  http://scrapmaker.com/data/wordlists/twelve-dicts/readme.html
- The dictionary contains 39587 words that are just lowercase letters
- This yields 39587^4 or 2455898220294264000 possible passwords
- That's about 61 bits of entropy