Added 'SeparatedOutput' command to capture stdout and stderr separately

[AriSweedler]

I just copy/pasted the code you already had but allowed a channel for stderr. Had to wrestle with the type checker, so that's why all the code I added is duplicate.

The interesting part is here

 	c.Session.Stdout = &stdout_buff
	c.Session.Stderr = &stderr_buff

And now I don't have to lose any information when running remote commands that may have stdout and stderr.