This function is a wrapper for the hist function in
the base package, permitting percentage scaling of the
vertical axis in addition to frequency and density scaling.
This function is modified from the Hist() function in the Rcmdr package.
HistEZR() package in RcmdrPlugin.EZR uses hist2() insted of hist(). In hist2(),
the method to set breakpoints between histogram cells was changed from
"Sturges" to "Scott".