RateLimiter introduced. Default codec now encodes length in 4 bytes.

- New BinaryUnit conversion class;
- Added https://github.com/bbeck/token-bucket/ as a dependency;
- New TokenBucketLimiter for rate limiting;
- Refactor of MessageCodec, now no longer Cloneable;
- Refactor of both MessageChannel and MessageServerChannel builders,
  MessageServerChannel builders now take Factories;
- Reimplementation of ChecksumCodec to wrap any other MessageCodec;
- DeflateCodec and LZ4CompressionCodec now encode length as 4 bytes;
- Fixed registration bug for UDPChannel;
- Updated TCP and UDP demos to use rate limiting;
- Updated codec unit tests.