Fix getGoDocString for go>=1.13

The go documentation formatting has been changed slightly in go 1.13.
This commit takes care of these changes.

cuda: update wrappers

re-compile dmi_wrapper

bench: add GTX 980 Ti results

work around cufft bug

This is the first mumax "community" release. It features Ahmad Syukri…

… bin Abdollah's conjugate gradient minimizer.

Final version of mumax.

v3.8beta1 fixes the closure caveat and an output race condition