convert images to binary and link them in

[gordonjcp]

Instead of storing the images as binary-converted-to-C-source with big lists of numbers, it's possible to turn them into a "linked library" which is just a blob with symbols that the compiler can recognise.

This PR is a proof-of-concept but it needs the Makefile written to create the binary image.

To use it, run "makeimage.sh" in the Nekobi plugin directory.

Everything will look the same.

Do something to the background graphic, re-run makeimage.sh, and recompile. The background will have changed.