adding missing single headers #941

Job	Run time
Cygwin GCC (x1)	59m 43s
FreeBSD Clang (x0.5)	19m 12s
MinGW GCC (x0.5)	44m 49s
macOS GCC with BLAS (x3)	35m 31s
MSVC (x1, excl test)	25m 59s
Nemo.jl	13m 58s
Ubuntu Clang (x5)	33m 6s
Ubuntu GCC via CMake (no check)	11m 18s
Ubuntu GCC, default flags with AVX2, Code Coverage (x10)	43m 46s
Ubuntu GCC (assert, x2)	21m 27s
	5h 8m 49s

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