Merge pull request #67 from junghans/patch-2 #159

Job	Run time
heffte (cmake, BUILTIN, cpu_intel)	1m 21s
heffte (cmake, FFTW, cpu_intel)	2m 0s
heffte (cmake, MKL, cpu_intel)	1m 56s
heffte (spack, BUILTIN, cpu_intel)	12m 6s
heffte (spack, FFTW, cpu_intel)	22m 37s
heffte (spack, MKL, cpu_intel)	12m 20s
heffte (cmake, ONEAPI, gpu_intel)	1m 34s
heffte (cmake, CUDA, gpu_nvidia)	5m 38s
heffte (spack, CUDA, gpu_nvidia)	16m 41s
heffte (cmake, ROCM, gpu_amd)	41s
	1h 16m 54s

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