Observing system

To increase the observing efficiency, all exposure commands (including dark exposures) have now a flag (``-f'') implemented which returns the prompt to the system during readout. A further improvement is to include this option in dither scripts such that the telescope offset is done during CCD readout. This was tested using full frame readout, but there are timing issues when small detector windows are used (i.e. when the readout time is only a few seconds).