Add input configuration to Config

It's a new node "input" that, if taking a name, includes the specific
input device the block should apply to. If no name is supplied,
the block applies to all inputs. Order matters and later config blocks
can override previous ones.

The config isn't actually used yet.

examples/config.kdl

@@ -69,4 +69,15 @@ pointer_binds {
     // tiled windows will automatically float if resized
     resize_window Mod4 BTN_RIGHT
 }
+// Default input config for all devices
+input {
+    accel_profile "flat"
+}
+// Framework 13 Touchpad
+input "PIXA3854:00 093A:0274 Touchpad" {
+    accel_profile "adaptive"
+    click_method "clickfinger"
+    natural_scroll "enabled"
+    tap "disabled"
+}