KAPPA: Parameter control of bin width in HISTOGRAM.

There is a new parameter called WIDTH which can be set instead of
NUMBIN.  It's currently defaulted to null to give the previous
behaviour.
KAPPA: Tidying in histogram.f.
KAPPA: Mention the now two ways to define bin width in the Description.
KAPPA: Typography and trailing space.
KAPPA: Note the constraint on Parameter WIDTH in HISTOGRAM.