Change rgl.* calls to *3d calls.

[dmurdoch]

Some upcoming changes to the rgl package will require changes to
fsbrain. I will be deprecating a number of rgl.* function calls.
You can read about the issues here:

  https://dmurdoch.github.io/rgl/articles/deprecation.html

I have made the required changes to fsbrain in the attached patches. These
changes should work with both old and new rgl versions.

I doubt if these will have any effect on #46, but it might be worth trying them out. As I commented there, the sample code dies very early on my system before any graphing, so it might be completely unrelated to rgl.

[dfsp-spirit]

Thanks a lot for the heads-up and PR, I will check it out.