cmd: stderr output not returned

[vranki]

Error output of the commands is not returned to user. Test with ls /asdfasdf doesn't return the error message it should.

[xPMo]

My bot's !eval supports stdout, stderr, and exit code. I don't use !cmd, so I don't know what information is typically important. Just consider this permission to lift and take whatever formatting logic you want from !eval.

Sidenote; I'd recommend adding the timeout handling, since commands can print something before timeout.