Change EOF behavior
Make it so that after the last file-defined pixels, the rest of the pixels in
the bitmap are undefined, and the last pixel in the image is the size of the
file. This code hasn't had rigorous testing, and I know there's still bugs in
it, but I think it's getting pretty close to a form I can merge into master.
The makefile test needs to be changed (and the tests can actually mean
something now), and the documentation updated.