Bump version to 0.8.1 #920

Job	Run time
msrv (ubuntu-latest)	10s
Clippy	40s
msrv (macos-latest)	23s
Build+test (stable, ubuntu-latest)	1m 31s
Clippy (Nightly)	40s
msrv (windows-latest)	47s
Build+test (beta, ubuntu-latest)	1m 40s
Check for documentation errors	11s
Build+test (nightly, ubuntu-latest)	1m 37s
Format	10s
Build+test (macos-latest, stable)	1m 51s
Check minimum versions of direct dependencies	16s
Check semver compatibility	2m 23s
Build+test (windows-latest, stable)	4m 10s
	16m 29s

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