hammerspoon: add auto-adjusting layouts
hammerspoon: add auto-adjusting layouts

And hot-keys to test them. This brings us pretty much to parity
with what I had in Slate, with the added bonus of a nice HUD alert
when testing the layouts.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent