History: Scalers for GEn

First I'll punt and point to [http://hallaweb.jlab.org/equipment/daq/THaScaler.html|Bob Michael's] general page on the THaScaler class.

What is in the GEN tree (and ))TTree(( variables "gen_" that are just copies)
is actually defined by the ))THaScaler(( class. The different
"trigger" types are pretty clear, however be aware that by default
everything except -+~~red:dclock~~+- is stored in the TTree as a "RATE". The -+~~red:clock~~+- variable is just the counting of the actual clock signal, divided by the time (in seconds) so that gives you the 105kHz frequency. The -+~~red:dclock~~+- variable I recently added to the class is the number of clock-cycles that the scaler event covers, and is present so we can get back from the rates to actual trigger yields and accumulated charges.