added twitter option

Added an a twitter option for lechbot.
Require 'twitter' to work.

added:
Twitter.configure do |config|
  config.consumer_key = YOUR_CONSUMER_KEY
  config.consumer_secret = YOUR_CONSUMER_SECRET
  config.oauth_token = YOUR_OAUTH_TOKEN
  config.oauth_token_secret = YOUR_OAUTH_TOKEN_SECRET
end
to config.rb .