Add CMUS info to tmux statusline. Mod zsh prompt.

tmux.conf, tmux/music.sh
	-Add `CMUS` music (artist name, song title, etc.) information to
	the `tmux` statusline.

zsh/prompt.zsh
	-Rename `ssh_info()` to `user_info()` and remove its `ssh`
	detection, because it's worth displaying the user/host-names
	whenever they're not those of my standard account.