add simple bytebeat example to test first implementation with

examples/curlywas/bytebeat.cwa

@@ -0,0 +1,10 @@
+include "../include/microw8-api.cwa"
+
+export fn upd() {}
+
+export fn snd(index: i32) -> f32 {
+    let inline saw = index & 255;
+    let inline env = (-index #>> 9) & 255;
+    let inline sample = saw & env;
+    sample as f32 / 255 as f32 - 0.5
+}