mod(example/input): reorder input handling cases; add alt-b/f binding implementations

examples/continuous.zig

@@ -87,10 +87,6 @@ const InputField = struct {
             .key => |key| {
                 if (key.isAscii()) try this.input.append(key.cp);
 
-                // TODO support arrow keys for navigation?
-                // TODO support readline keybindings (i.e. ctrl-k, ctrl-u, ctrl-b, ctrl-f, etc. and the equivalent alt bindings)
-                // create an own `Element` implementation from this
-
                 if (key.eql(.{ .cp = zterm.input.Enter }) or key.eql(.{ .cp = zterm.input.KpEnter }))
                     this.queue.push(.{ .accept = try this.input.toOwnedSlice() });