Parse standards-formatted text into slack-specific mishmash

[sdhull]

A casual google reveals at least four javascript libraries that offer parsing from standards-based text (markdown, html) into whatever the heck it is that slack accepts (some mishmash of markdown and angle-brackets links, • characters instead of lists, etc) [1, 2, 3, 4].

This gem (or some other gem in this org?) should offer similar, officially-support functionality, in order to make it trivially simple to send html or markdown to the Slack API.

[dblock]

I agree. We already offer some message parsing, so why not message mishmashing. In fact I insist we call it this way, too :) client.mishmash(s)

Looking forward to PRs!