support json_name proto annotation for renaming field names in GraphQL schema.

also bumping version to release 0.2.1.

Author: siderakis

rejoiner/src/test/proto/test_proto.proto

@@ -26,6 +26,7 @@ message Proto1 {
   InnerProto test_inner_proto = 4;
   //Some leading comment
   int64 camelCaseName = 5;
+  string name_field = 6 [json_name="RenamedField"];
 
   message InnerProto {
     string foo = 1;