Add support for custom attributes #2343

Job	Run time
minimal	17s
quickchecking	15s
msrv	51s
docs	18s
rustfmt-clippy	26s
check-cfg	21s
test (ubuntu-latest, 9.0, 1, 0, 0, 0, 0)	1m 50s
test-book	5s
test-expectations (ubuntu-latest)	43s
test-expectations (macos-12)	1m 9s
test (ubuntu-latest, 9.0, 1, 0, 0, 1, 0)	1m 42s
test (ubuntu-latest, 9.0, 1, 0, 1, 0, 0)	1m 33s
test (ubuntu-latest, 9.0, 1, 0, 1, 1, 0)	1m 39s
test (ubuntu-latest, 9.0, 1, 1, 0, 0, 0)	1m 51s
test (ubuntu-latest, 9.0, 1, 1, 0, 1, 0)	1m 50s
test (ubuntu-latest, 9.0, 1, 1, 1, 0, 0)	1m 49s
test (ubuntu-latest, 9.0, 1, 1, 1, 1, 0)	1m 50s
test (ubuntu-latest, 16.0, 1, 0, 0, 0, 0)	1m 50s
test (ubuntu-latest, 16.0, 1, 0, 0, 1, 0)	1m 52s
test (ubuntu-latest, 16.0, 1, 0, 1, 0, 0)	1m 51s
test (ubuntu-latest, 16.0, 1, 0, 1, 1, 0)	1m 52s
test (ubuntu-latest, 16.0, 1, 1, 0, 0, 0)	1m 52s
test (ubuntu-latest, 16.0, 1, 1, 0, 1, 0)	1m 50s
test (ubuntu-latest, 16.0, 1, 1, 1, 0, 0)	1m 52s
test (ubuntu-latest, 16.0, 1, 1, 1, 1, 0)	1m 56s
test (ubuntu-latest, 16.0, 0, 0, 1)	1m 52s
test (macos-12, 9.0, 0, 0, 0)	1m 28s
success	1s
	36m 45s

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