slurm 0.4.0 (new formula)

Add a formula for slurm, an ncurses network load/traffic monitor.
https://github.com/mattthias/slurm
@mikemcquaid Unfortunately, neither that patch, nor https://github.com/return/slurm/commit/68223154be577aac60702723ece7ac7c89e92998 will patch against the 0.4.0 release. I collapsed the 4 diffs in https://github.com/mattthias/slurm/pull/2 into this one small patch because 3/4 are irrelevant, and the other will only patch against HEAD.