calculates histogram for each column
[H,X] = nan_histo(Y,Mode)
frequency of each row
single bin-values (default Mode)
separate bin-values for each column
if one input parameter is 'plot', the histogramm bar(X,H) will be plotted
are the bin-values
is the frequency of occurence of value X
more histogram-based results can be obtained by hist2res
C.E. Shannon and W. Weaver "The mathematical theory of communication" University of Illinois Press, Urbana 1949 (reprint 1963).