brew: add hammerspoon
brew: add hammerspoon

Will give this a try, seeing as I am setting up a new
machine, and Slate is long since abandonware.

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