tmux — split screens, sessions, never lose work

Prefix is `Ctrl-b` by default.

## Sessions
`tmux new -s name` — start named session
`tmux ls` — list sessions
`tmux attach -t name` — reattach
`Ctrl-b d` — detach
`tmux kill-session -t name`

## Windows
`Ctrl-b c` — new window
`Ctrl-b ,` — rename current window
`Ctrl-b n` — next / `Ctrl-b p` — prev
`Ctrl-b 0..9` — jump to window N

## Panes
`Ctrl-b "` — split horizontal
`Ctrl-b %` — split vertical
`Ctrl-b arrows` — move between panes
`Ctrl-b z` — zoom pane (toggle)
`Ctrl-b x` — close pane