ENH: fix dead links in docs, remove subtract at boundary, check for CUDA, improve doctests, optimize for loop in divergence
ENH: fix dead links in docs, remove subtract at boundary, check for CUDA, improve doctests, optimize for loop in divergence

odlgroup/odl,kohr-h/odl,kohr-h/odl,aringh/odl,aringh/odl,odlgroup/odl