Try Elm: make links in compiler output clickable

[spikefoo]

Some compiler errors include links to hints, e.g.:

If you are seeing this error for the first time, check out these hints:
<https://github.com/elm-lang/elm-compiler/blob/0.18.0/hints/missing-patterns.md>
The recommendations about wildcard patterns and `Debug.crash` are important!

It would be nice if these links were clickable.

This issue applies to elm-reactor too.

I'll try to work on a PR later. (Links can probably be found by using a regex to find any HTTP(S) URLs in angle brackets)

[process-bot]

Thanks for the issue! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.