Treat signature as markdown, but process w/ nl2br extension

[nottwo]

Hi,

I guess the template idea from #2 wasn't too popular. How about just allowing the signature be .md?

My workplace has standardized on a rich signature that I have complied with by treating the sig as markdown and then adding appropriate styles:

**First Lastname**
Title
[800-555-0123](tel:800-555-0123)
_[company](company-url)_

Rather than splitting the signature by newlines & joining with <br>s, I process the signature with the nl2br extension so that text/plain format=flowed & md->HTML versions of the email are presented properly.

[Roguelazer]

want to write up a test for this?