add `go` script to install/update kitchenplan (inspired by homebrew)

installation script modeled after homebrew to automate setup and updating of kitchenplan.

supports custom forks of kitchenplan via environment variables.

example execution:
```bash
# (optional) use a custom kitchenplan repository
$ export KITCHENPLAN_REPO=https://github.com/mycompany/kitchenplan.git

# install/update kitchenplan recipes and run chef
 $ ruby -e "$(curl -fsSL https://raw.github.com/kitchenplan/kitchenplan/master/go)"
```

see updated README + go script for additional documentation.