no_std support, more minimal and less intrusive version #247

Job	Run time
32bit tests	23s
Build & test (ubuntu-latest, stable)	43s
Build & test (ubuntu-latest, beta)	33s
Verify benchmarks compile	36s
Check it compiles on old Rust (1.31.0)	3m 29s
Run the big ignored tests	1m 0s
Build & test (ubuntu-latest, nightly)	31s
Build & test (macos-latest, stable)	53s
Clippy lints	15s
Build & test (macos-latest, beta)	1m 5s
Test with experimental-thread-local	53s
Check documentation links	14s
Build & test (macos-latest, nightly)	54s
Build & test (windows-latest, stable)	3m 17s
Miri checks	5m 49s
Check formatting	16s
Build & test (windows-latest, beta)	1m 54s
Check it compiles on old Rust (1.45.0)	10s
Build & test (windows-latest, nightly)	1m 40s
Thread Sanitizer checks MacOS	7m 24s
	31m 59s

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