Add doxygen #59

Job	Run time
lint	11s
check_docker_files / check_docker_files	4s
build_base	0s
build (openmp, gcc, gcc, g++, -DKokkos_ENABLE_OPENMP=ON, native)	4m 0s
build (threads, gcc, gcc, g++, -DKokkos_ENABLE_THREADS=ON, native)	2m 54s
build (serial, gcc, gcc, g++, -DKokkos_ENABLE_SERIAL=ON, native)	4m 4s
build (cuda, nvcc, gcc, g++, -DKokkos_ENABLE_CUDA=ON -DKokkos_ARCH_AMPERE80=ON, native)	7m 10s
build (cuda, nvcc, gcc, g++, -DKokkos_ENABLE_CUDA=ON -DKokkos_ARCH_AMPERE80=ON, host_device, -DKo...	8m 35s
build (hip, rocm, hipcc, hipcc, -DKokkos_ENABLE_HIP=ON -DKokkos_ARCH_VEGA90A=ON, native)	8m 27s
build (hip, rocm, hipcc, hipcc, -DKokkos_ENABLE_HIP=ON -DKokkos_ARCH_VEGA90A=ON, host_device, -DK...	8m 35s
build (sycl, intel, icx, icpx, -DKokkos_ENABLE_SYCL=ON -DKokkos_ARCH_INTEL_GEN=ON, native)	12m 36s
build (sycl, intel, icx, icpx, -DKokkos_ENABLE_SYCL=ON -DKokkos_ARCH_INTEL_GEN=ON, host_device, -...	12m 8s
test (cuda, nvcc, self-hosted, cuda)	11m 4s
test (openmp, gcc, ubuntu-latest)	2m 42s
test (threads, gcc, ubuntu-latest)	2m 49s
test (serial, gcc, ubuntu-latest)	2m 50s
	1h 28m 9s

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