Add externs file for closure type checking

Author: inexorabletash

Diff for: util/externs.js

@@ -0,0 +1,28 @@
+//
+// Externs for Closure Compiler
+// https://developers.google.com/closure/compiler/
+//
+// Usage:
+//   java -jar compiler.jar \
+//     --jscomp_warning reportUnknownTypes \
+//     --warning_level VERBOSE \
+//     --summary_detail_level 3 \
+//     --externs util/externs.js \
+//     lib/encoding.js
+//
+
+/**
+ * @param {string} name
+ * @return {*}
+ */
+function require(name) {}
+
+/**
+ * @type {Object}
+ */
+var module;
+
+/**
+ * @type {Object.<string,*>}
+ */
+module.exports;