Added hg_summary_cb, which writes statistical outputs using climatology_bounds

h1_summary_cb - computes means and standard deviations of hourly output
netCDF files, creating two new netCDF files (one for the means and one
for the standard deviations) for each month by hour of day, just like
h1_summary and h1_summary2. However, this version does not create a
new "hour" dimension on every output field. Instead, it follows the
CF-1.0 standard that requires a "climatology_bounds" variable (instead
of the normal "time_bounds" variable) and each hour-of-day mean/standard
deviation is stored as a time slice.

h1_summary_cb will be used for the remaining C-LAMP experiments, starting
with Experiment 2.2.