Add typescript declaration file.

Author: ry

v8worker2.d.ts

@@ -0,0 +1,6 @@
+declare namespace V8Worker2 {
+  function print(...args: any[]): void;
+  type RecvCallback = (ab: ArrayBuffer) => void;
+  function recv(cb: RecvCallback): void;
+  function send(ab: ArrayBuffer): null | ArrayBuffer;
+}