[dev] [surf] Patch: horizontal scroll

Howdy, folks,

I'm a new subscriber, and thought I'd start with a patch.
The attached patch adds horizontal scrolling to surf, mainly
so that it can be bound to a key aside from the arrow keys.

The function `scroll()' has been renamed to `vscroll()', and
a new function called `hscroll()' has been added.

As a warning, to keep the scrolling keybinds consistent
(left on l, right on h), navigate() keybinds have been moved
to MODKEY+b for backwards navigation & MODKEY+f for forwards
navigation.

Thanks a lot, and I hope this is useful.

Ivy Foster