Add useMousePosition hook

src/machinery/useMousePosition.js

@@ -0,0 +1,16 @@
+import { useEvent } from '/machinery/useEvent'
+
+export function useMousePosition(onMouseMove) {
+  const callback = useEvent(onMouseMove)
+
+  React.useEffect(
+    () => {
+      window.addEventListener('mousemove', handleMouseMove)
+      return () => window.removeEventListener('mousemove', handleMouseMove)
+      function handleMouseMove(e) {
+        callback({ x: e.clientX, y: e.clientY })
+      }
+    },
+    [callback]
+  )
+}