v2.10.1

d883e04 Support build darwin
ca7dcda Optimized version management
d75ef1b Log to /var/log/rttys.log when stdout is a terminal
87a9248 Handle some error
2b10e61 Drop code which is not needed.

pre-built release binaries:
rttys-darwin-386.tar.gz
rttys-darwin-amd64.tar.gz
rttys-linux-386.tar.gz
rttys-linux-amd64.tar.gz
rttys-windows-386.zip
rttys-windows-amd64.zip