correctly determine beginning and end of cmd output in send_cmd

[N-Coder]

and return output in correct order instead of in reverse.

Instead of relying on the command being complete after 1 second and then going through the log in reverse to find the beginning, we now place two unique beginning and end markers in the log file. This allows us to

• read the log file in the correct order
• get all output of the command in real time, even if it takes a little longer to complete
• return immediately if the command completes early, instead of always waiting for a constant time of 2 seconds
• prevent head aches for future self

Please note that:

• this still won't filter out output which is not generated by the sent command (which is not possible without factorio tagging its output)
• the NONCMDPATTERN filter is no longer included as it should be optional (at least in my opinion). Hint: to filter out any garbage such as empty lines, server debug output and these markers, the following code could be used (in this case in tail_chatlog, as the output generated by send_cmd between the markers is also removed)

  stdbuf -i0 -o0 tail -F -n 0 ${CMDOUT}\
   | stdbuf -i0 -o0 sed "/^\s*$/d"\
   | stdbuf -i0 -o0 egrep -v "${NONCMDPATTERN}"\
   | stdbuf -i0 -o0 egrep -v "Player FACTORIO_INIT_CMD_DELIMITER doesn't exist."\
   | stdbuf -i0 -o0 awk -v flag=1 "/Player FACTORIO_INIT_CMD_[0-9]+_START doesn't exist./{flag=0}\
      /Player FACTORIO_INIT_CMD_[0-9]+_END doesn't exist./{flag=1;next}\
      flag"

This also fixes #116