Implement mw.command for defining new commands (bind replacement)

Define a new command ,boop handled by boopCmd:

    function boopCmd(arg1, arg2, arg3)
    {
            mw.print("Arg 1: " + arg1);
            mw.print("Arg 2: " + arg2);
            mw.print("Arg 3: " + arg3);
    }
    mw.command.boop = boopCmd;