2.3

Auto-hide and hide navigation buttons

New opt-in options: auto-reveal the back/forward/reload buttons on hover
(or hover + focus), or hide them entirely for shortcut / mouse-button users.

Configure in CONFIG:

• --uc-autohide-nav-buttons: 0 = always show, 1 = reveal on hover and focus, 2 = reveal on hover only
• --uc-hide-nav-buttons: 1 = hide back/forward/reload entirely

Big thanks to @DeathMurderGod for implementing this in #22, great work on a
first contribution. Polished in #23, which finally closes the long-standing #12.