Add support for custom attributes #2344

Job	Run time
msrv	51s
docs	25s
minimal	11s
rustfmt-clippy	26s
check-cfg	23s
quickchecking	14s
test (ubuntu-latest, 9.0, 1, 0, 0, 0, 0)	1m 44s
test (ubuntu-latest, 9.0, 1, 0, 0, 1, 0)	2m 5s
test-book	7s
test (ubuntu-latest, 9.0, 1, 0, 1, 0, 0)	1m 55s
test-expectations (ubuntu-latest)	45s
test-expectations (macos-12)	54s
test (ubuntu-latest, 9.0, 1, 0, 1, 1, 0)	1m 43s
test (ubuntu-latest, 9.0, 1, 1, 0, 0, 0)	2m 14s
test (ubuntu-latest, 9.0, 1, 1, 0, 1, 0)	3m 3s
test (ubuntu-latest, 9.0, 1, 1, 1, 0, 0)	2m 1s
test (ubuntu-latest, 9.0, 1, 1, 1, 1, 0)	2m 8s
test (ubuntu-latest, 16.0, 1, 0, 0, 0, 0)	2m 31s
test (ubuntu-latest, 16.0, 1, 0, 0, 1, 0)	2m 30s
test (ubuntu-latest, 16.0, 1, 0, 1, 0, 0)	2m 34s
test (ubuntu-latest, 16.0, 1, 0, 1, 1, 0)	2m 34s
test (ubuntu-latest, 16.0, 1, 1, 0, 0, 0)	2m 59s
test (ubuntu-latest, 16.0, 1, 1, 0, 1, 0)	2m 55s
test (ubuntu-latest, 16.0, 1, 1, 1, 0, 0)	3m 11s
test (ubuntu-latest, 16.0, 1, 1, 1, 1, 0)	2m 58s
test (ubuntu-latest, 16.0, 0, 0, 1)	2m 4s
test (macos-12, 9.0, 0, 0, 0)	1m 52s
success	1s
	47m 18s

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