added some tools to graphically examine snapshots, as well as plot boxes on them to illustrate focus areas
added attenutate_dem.pro, which allows dem peaks to be rescaled as a percentage of the max peak height
added dem_diff.pro which provides a facility to calculate a dem curve that is the difference between two curves, takes errors into account
compare_dems.pro: added facility to compare_dems as relative peak strengths, as well as making some minor tweaks to legend size, colours and linestyles
fixed problem where exit was requested at the event level not file level, would cause an exception
tightened SNR constraint in dem reconstruction but added override for 'faint' phenomena