Rust

Update CI, add note about MSRV, fix Clippy #115

Job	Run time
get-package-info	6s
bench-lints	17s
docs	15s
regen	10s
lints	34s
build_test (ubuntu-latest, 1.36)	5m 13s
build_test (windows-latest, 1.36)	7m 44s
build_test (ubuntu-latest, nightly)	22s
build_test (ubuntu-latest, beta)	22s
build_test (windows-latest, nightly)	1m 19s
build_test (ubuntu-latest, stable)	23s
build_test (windows-latest, beta)	46s
build_test (windows-latest, stable)	56s
	18m 27s

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