Implement "not" semantics for specifying which aspects to install

[wincent]

Use case

On a machine that is already set-up, I want to re-install everything except the homebrew aspect, because that one is terribly slow.

Workaround

For now, I do this:

1. Run ./install
2. When it gets to the Homebrew prompt (this is the one interactive part of the install), abort.
3. Run the rest of the install by spelling out all the aspects that follow the homebrew one; ie:

   ./install iterm node karabiner launchd ruby shell ssh tampermonkey terminfo nvim cron automator automount defaults
   

Desired alternative

What I'd like to be able to do is:

./install '!homebrew'

or:

./install ^homebrew

ie. the semantics would be "whatever aspects you were going to install, subtract this one from it. That is ./install nvim dotfiles ^nvim, although pointless, would be equivalent to ./install dotfiles.