A implement of Dart:convert for [Protobuf](https://developers.google.com/protocol-buffers/).
All the function seem to completed, So the next, We will hard test it.
Correct the problem for publication.
- Added to support Dart:Convert.
- Now it seems that most of the bugs have been solved.
- Some problems have been solved, mainly those brought about by the rewriting process.
- Conduct detailed tests to find problems.
- Convert my protobuf library from C++ to Dart, It's the initial version for Dart version protobuf.