A previous commit intended to remove the old PNGS and just leave the
new ones, but neglected to add the new ones resulting in the deletion
of all the PNGs. Um... oops.
The update to the new design accidentally left some old images. The new
design doesn't include resources for images we alias, and when the
directory was updated I forgot to remove the images corresponding to the
aliases.
The bitmap emoji tools are extended to create GSUB rules for character
sequences. The images are renamed to code the character sequence in their
filenames. New images are created for ASCII digits and number sign. A new
script is added to add cmaps to the files for backward compatibility.