Motivation:

Netty was missing support for Protobuf nano runtime targeted at
weaker systems such as Android devices.

Modifications:

Added ProtobufDecoderNano and ProtobufDecoderNano
in order to provide support for Nano runtime.

modified ProtobufVarint32FrameDecoder and
ProtobufLengthFieldPrepender in order to remove any
on either Nano or Lite runtime by copying the code
for handling Protobuf varint32 in from Protobuf
library.

modified Licenses and NOTICE in order to reflect the
changes i made.

added Protobuf Nano runtime as optional dependency

Result:

Netty now supports Protobuf Nano runtime.