Enable compilation with #![no_std] #58

Job	Run time
Test (stable)	2m 20s
Test (beta)	2m 24s
Test (nightly)	2m 27s
Test (linux32)	2m 39s
Test (macos)	20s
Test (aarch64-ios)	22s
Test (win32)	1m 20s
Test (win64)	2m 25s
Test (mingw64)	1m 10s
Test (windows-latest)	2m 38s
Test (stable-no-std, ubuntu-latest, stable, x86_64-unknown-linux-gnu, --no-default-features)	2m 18s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc)	1m 43s
	22m 6s

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