Feat: #4 Added 'markdown', 'call' and 'email'

[legovaer]

As requested in #4, I added the fields that allow users to format messages as Markdown. In order to enable Markdown, a user just has to add any string / boolean to the 'markdown' data field:

data:
  markdown: Yes

I implemented it this way so that we don't have to deal with validating the input.