v3.1.0
rename RLPEncoder.encode to encodeString;
add RLPOutputStream;
add RLPItem.exportData(OutputStream);
add RLPItem convenience methods for functional style programming;
SHA-256 (headlong-3.1.0.jar): a833f33c8b98dc95f98c2529d4f6e8185e7703901e3b38493c0fd1b86ab43c65