[slim-vim] Compiler Notes

[Brad Beveridge]

One of the next items I am planning on tackling is handling compiler
notes, which are warnings/errors/style warnings, etc.
Emacs Slime groups the warnings together in a folded up tree, much like
[+] Errors
[-] Warnings
     - Warning1
     - Warning2

I can emulate this behaviour, if we really really want it.  But I was
thinking we probably ought to stick to the Vim way of error handling
(:help quickfix).  I'll order the warnings/errors so the errors are
first, and then in decreasing order (probably warnings then
style-warnings).
Thoughts?

Cheers
Brad