In two steps I tried to improve the `main()` function. The reason for those patches is that the current `main()` function is doing much more than the necessary (implementing commands); this makes the code not uniform and less clear.
Tests Since those patches are mainly, copy & paste and re-writing how `trace-cmd` runs command, I tested these changes by executing the help message for all the commands. In principle, if we are able to run the commands the patches are correct.
