Don't use Markdown-formatted links in email

[jeffhandley]

As they don't work in plain-text mail clients.

[analogrelay]

Unfortunately this is le hard, as we discussed in person. The problem is that if we change the markdown to just have the URL inline, it renders underscores in it as Italics, etc.

The real solution is to just have two templates, HTML and Plain Text. We will be revamping our email infrastructure during APIv3 and can do that then.