- removed spurious check in decrypt() against blocksize
- added additional tests for small sized blocks and inputs smaller than
the blocksize.
- updated README to capture dependencies (protobuf tools)
- aead nonce construction is efficient (replace last 8 bytes of salt
with encoded block# and chunk-size
- increase aead nonce size to 32 bytes
- refactor errors into a separate file
- update "build" to latest version
- updated README.