This reduces the amount of logic built into the generated code. If we
swap to an alternative form of decoding we should have greater ability
to adapt the existing API to make use of the new one. Previously most
changes would require duplicating all the nano marshalling code.
- Rename flushTo() to drainTo().
- Remove flushTo() from DeferredNanoProtoInputStream (which is renamed
to NanoProtoInputStream), because the optimization is not implemented.
- Rename DeferredProtoInputStream to ProtoInputStream.
#529
io.grpc.nano sort of seems like a "small" version of grpc-java. And
io.grpc.proto could also mean multiple things. Using "protobuf"
and "protobuf nano" gets us consistent names that are still
understandable, predictable, and more similar to protobuf project
itself.