Added support for html and markdown messages
  Allow reply messages to be formatted in html or markdown
  Format is configurable with and environment variable. Plaintext by default
Improved detection if the user needs to reauthorize hubot
  It now detects if the token we have is for the currently configured application ID in case it changes
Merge pull request #24 from tspascoal/master

Added support for html and markdown messages (issue #22)