add `--disc-menu` option
add `disc-menu-active` property
add `discnav` command with the `up`, `down`, `left`, `right`, `select`,
`menu`, `title-menu`, `popup`, `audio-menu`, `sub-menu`, `angle-menu`,
`up-menu`, `prev`, `red`, `green`, `yellow`, `blue`, `mouse-move` and
`mouse-click` actions