Serialize/Deserialize slices without length prefix with break-change

[ScarboroughCoral]

Following:

• issue: https://github.com/tafia/quick-protobuf/issues/202

• pr: https://github.com/tafia/quick-protobuf/pull/208

  • [x] Message writer without prefixing a length
  • [x] Slice serializer without prefixing a length
  • [x] Reading messages that aren't prefixed with a length
  • [ ] pass test for all the above implementations

[ScarboroughCoral]

I want to fix this issue, but there are something error when testing the code. I think there are some code need to fix in the pb-rs folder, such as pb-rs/src/types.rs