Add support for Subtle and DER. #892

Job	Run time
Cargo deny check	18s
Clippy	43s
Feature checks	1m 18s
Docs	45s
Fmt	13s
test (stable, --no-default-features)	1m 35s
test (stable)	1m 30s
test (stable, --all-features)	55s
test (beta, --no-default-features)	1m 34s
test (beta)	1m 31s
test (beta, --all-features)	58s
test (nightly, --no-default-features)	1m 27s
test (nightly)	1m 29s
test (nightly, --all-features)	59s
test (1.65, --no-default-features)	1m 10s
test (1.65)	1m 13s
Accept	0s
	17m 38s

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