Move away from termbox, tmux compatibility

[jinnatar]

On latest 0.7.5:

%> ./ctop-0.7.5-linux-amd64 
panic: termbox: error while reading terminfo data: termbox: unsupported terminal [recovered]
        panic: termbox: error while reading terminfo data: termbox: unsupported terminal

goroutine 1 [running]:
main.panicExit()
        /home/bradley/work/bcicen/ctop/main.go:147 +0x6b
panic(0xaf0de0, 0xc0001c0e70)
        /usr/lib/go/src/runtime/panic.go:969 +0x1b9
main.main()
        /home/bradley/work/bcicen/ctop/main.go:104 +0x9a7
%> echo $TERM 
tmux-256color

The issue seems to stem from nsf/termbox-go/issues/215 which is already several years old and is not getting fixed.
The project in fact is in maintenance mode:
"This library is somewhat not maintained anymore. " ... " If you're looking for a Go lib that provides terminal-based user interface facilities, I've heard that gdamore/tcell is good ..."

Ergo, to fix this issue the solution is probably to move away from termbox, perhaps to tcell.

A workaround in the meanwhile is to lie in .tmux.conf and use screen termcap, but this causes other issues:

set -g default-terminal screen-256color

[xbb]

Another workaround is to use an alias like:

alias ctop='TERM="${TERM/#tmux/screen}" ctop'

[mbirth]

Or in fish:

alias ctop='TERM="(string-replace tmux screen $TERM)" /usr/bin/ctop'

Make it permanent with funcsave ctop afterwards.