Support ANSI escape codes/custom colors

Trying to use escape codes doesn't work as I would have hoped:

```
color_on = '\033[32m'
color_off = '\033[39m'

menu_item = MenuItem("{0}Menu Item{1}".format(color_on, color_off))
```

Result:

```
   1 - ^[[32mMenu Item^[[39m
```

Thanks...
