Update keogram.cpp
Update keogram.cpp

Fixes #881 
* Allow users to turn off displaying date via new -D option.
* Added #define's for annotation arguments (date, hour, etc.)
* Replaced "prevHour" check with check if we already added the current hour to the annotation list.  The old method would miss hours when run in multi-processor mode.
* Date is always displayed - at the 0 hour if possible, otherwise right-justified.  It used to only be displayed if there was a 0 hour.
* Minor optimization - put column in new "column" variable rather than recalculate it multiple times.  This also makes the code easier to read and maintain.
* Display warning message if an hour or date label can't be displayed.
thomasjacquin/allsky,thomasjacquin/allsky,thomasjacquin/allsky