yabai3: i3 sanity wrapper around yabai

[sebastianst]

yabai3 is a simple zsh script that provides a few commands which imitate the way i3 behaves under the same action, but uses yabai to accomplish the intended effects.

Among a few others, it provides focus, move, and resize commands that imitate the same commands of i3. In particular, they are stack-aware.

Feedback and PRs welcome!

[qhsong]

Nice Work~