Keybindings for Linux/Windows

0. Add keybindings for Linux and Windows (`Alt` instead of `Cmd`).
0. Add keybinding to destroy active term (`Cmd-Shift-x` / `Alt-Shift-x`).
0. Toggle keybinding now works if we have no active terms (destroyed all old ones).
0. Some code cleanup, coffeelint compliant.

I'm creating `clean` right now, stay tuned (will push to this PR).