Add an environment variable to enable markdown

[dfyx]

Kind of related to #9

It would be really cool to have an environment variable like FORMATTING=markdown to enable markdown in messages.

Some ideas what could be done with that:

• Link user names to their profiles
• Inline links that are currently in parentheses
• Link project names

[dfyx]

A simple way to handle this would be to always write markdown and use summarize-markdown to strip out all markdown when none is supported.

[spruce]

Good idea. the problem with that library would be that it completly strips the linktarget from links
https://github.com/bryanburgers/summarize-markdown/blob/master/index.js#L55-L57

[dfyx]

I'd say for some links (such as links to user profiles or even individual commits) that's the expected behavior but I agree that for some links, the target url should stay in the message.

The alternative would be to create dedicated renderer objects for every format.

[dfyx]

Also, some alternatives:

• strip-markdown
• remove-markdown