retired the plot_file_* options because they are not pertinent to this object; the plot_xlimits option now accepts datetime; fixed bug in the common_axis_limits method; minor revision of the legend method
retired the plot_file_* options because they are not pertinent to this object; the plot_xlimits option now accepts datetime; fixed bug in the common_axis_limits method; minor revision of the legend method

jgte/orb,jgte/orb,jgte/orb,jgte/orb,jgte/orb