Make test script executable.
Update CS dependency to 1.6.3
Expose Chunker.leftover buffer so mode-switching can be done.

For example, switching from newline-terminated mode to accepting all bytes
regardless of newlines. This cannot be done if the network link is very fast
and Chunker consumed all the bytes following the newlines even though the
splitting is no longer desired.
Update README and example.
0.2.1