Adds a quiet option to `start`

I use honcho to manage my application and I got sick of redid overwhelming the logs:

![screen shot 2013-07-31 at 8 32 52 pm](https://f.cloud.github.com/assets/1097953/891471/19f1ad3a-fa5b-11e2-853c-3f40a6e67a74.png)

As such, I figured I would add a quiet option, which could suppress output from particularly noisy processes. With the quiet option enable on redis, my log is much more manageable:

![screen shot 2013-07-31 at 8 35 03 pm](https://f.cloud.github.com/assets/1097953/891480/80256272-fa5b-11e2-9706-a5056d4353f5.png)

Usage is really easy:

    -q process1,process2
    --quiet process1, process2 

I've added tests to ensure functionality works.

Would love to hear people's thoughts!