v2.8.1

837b6c8 Fix bug: use null variable on window.atob
b753939 validate params for exec command on web
d813be2 Show stdout and stderr when exec cmd on web.
db9ea64 Add rttys.service for systemd
a5b38f0 Fix rttys.init

Precompiled:
rttys-linux-386.tar.gz
rttys-linux-amd64.tar.gz
rttys-windows-386.zip
rttys-windows-amd64.zip