Several features

This pull would add the following very features contributed by several people:

    -S            Screensaver mode                               
    -x            Show box                                       
    -b            Use bold colors                                
    -T tty        Display the clock on the specified terminal    
    -n            Don't quit on keypress                         
    -d delay      Set the delay between two redraws of the clock. Default 1s. 
    -a nsdelay    Additional delay between two redraws in nanoseconds. Default 0ns.