Also validate map fields, see #526 (this really needs some tests)

Author: dcodeIO

Diff for: README.md

@@ -440,6 +440,12 @@ JSON to/from buffer x 89,854 ops/sec ±0.79% (93 runs sampled)
         Type to/from buffer was fastest
         JSON to/from string was 49.0% slower
         JSON to/from buffer was 63.9% slower
+
+benchmarking verifying performance ...
+
+Type.verify x 5,941,014 ops/sec ±0.96% (90 runs sampled)
+
+                Type.verify was fastest
 ```
 
 Note that JSON is a native binding nowadays and as such is about as fast as it possibly can get. So, how can protobuf.js be faster?

Diff for: cli/targets/static.js

@@ -286,7 +286,9 @@ function buildType(ref, type) {
         "@param {" + fullName + "|Object} message " + type.name + " or plain object to verify",
         "@returns {?string} `null` if valid, otherwise the reason why it is not"
     ]);
-    buildFunction(type, "verify", codegen.verify.generate(type), {});
+    buildFunction(type, "verify", codegen.verify.generate(type), {
+        util : "$protobuf.util"
+    });
 }
 
 function buildService(ref, service) {