Axis titles!

Updated Plotter2D to automatically set the name of the x and y
axes to the names of the input variables and to set the title of
the histogram to "X_Variable vs. Y_Variable". Plotter1D sets the
name of the x axis and the histogram title to the name of the input
variable and the name of the y axis to "Counts per bin".

Changed the _help function of Executable to make it less likely
that the text will wrap to the next line when displaying.

Added optional argument (rescan) to Cut1D and cut2D to allow the
making of a cut without rescanning the data. By default, the data
is rescanned.