Added add blend, chroma key blend, colour blend, colour burn blend,
colour dodge blend, darken blend, difference blend, divide blend,
exclusion blend, hard light blend, hue blend filter, lighten blend,
linear burn blend, luminosity blend, mask filter, multiply blend,
overlay blend, saturation blend, screen blend, soft light blend, source
over blend, subtract blend, crosshatch, halftone, pixellate, polar
pixellate, and polka dot.  Added example project for all of the two
input blend filters.