Added: append_to_legend

Added command to append an entry to a legend.
Added bdc_color.m

Used to generate color-matrices wit ha starting and an ending
color. The only implemented mode is to let the colors vary
linearily from c1 to c2. This is a low level function used by
other functions.
Added bdc_color_even.m

Used to get colormaps with specified number of elements in each
bin. E.g. bdc_color_even(z, [ 0.1, 0.5]) would put in color
transitions in the color map in such a way that 10% of the
elements in z are in the first bin 50% - 10% = 40% in the next
and the last 50% in the last.
Help for bdc_color_even.m

Added some basic help.