ENH: Example of translating existing project

I need to do this anyway for SDF-on-shader support, figured I might as well make an example out of it. @almarklein @rougier if either of you have spare time, I could use a little bit of help. I don't quite understand how to get the FrameBuffer working properly. I translated the JFA code into `glfw` calls in `jfa_translation.py`. This should work fine. There are some artifacts related to the calculation that I know how to correct -- you can ignore those for now.

The real issue comes in `jfa_vispy.py`, where I try to use all `vispy` code to do the same. I can't seem to get it to produce the same result. Looking at the two bits of code, any ideas why?

Note that the `vispy` and `translation` versions use slightly different shaders, but the translation of parameters was pretty straightforward (and the normal-display/F2 mode works fine) so I don't *think* that's the issue.