Add https://github.com/os72/protobuf-dynamic

Add reference to Protocol Buffers Dynamic Schema (https://github.com/os72/protobuf-dynamic)

docs/third_party.md

@@ -146,3 +146,4 @@ There are miscellaneous other things you may find useful as a Protocol Buffers d
 * [ProtoBuf with Java EE7 Expression Language 3.0; pure Java ProtoBuf Parser and Builder.](https://github.com/protobufel/protobuf-el)
 * [Notepad++ Syntax Highlighting for .proto files](https://github.com/chai2010/notepadplus-protobuf)
 * [Linter for .proto files](https://github.com/ckaznocha/protoc-gen-lint)
+* [Protocol Buffers Dynamic Schema - create protobuf schemas programmatically (Java)] (https://github.com/os72/protobuf-dynamic)