Add support for custom attributes #2355

Job	Run time
minimal	10s
docs	25s
msrv	50s
quickchecking	13s
rustfmt-clippy	27s
check-cfg	21s
test-book	9s
test (ubuntu-latest, 9.0, 1, 0, 0, 0, 0)	1m 44s
test (ubuntu-latest, 9.0, 1, 0, 0, 1, 0)	1m 46s
test-expectations (ubuntu-latest)	52s
test (ubuntu-latest, 9.0, 1, 0, 1, 0, 0)	1m 46s
test-expectations (macos-12)	1m 16s
test (ubuntu-latest, 9.0, 1, 0, 1, 1, 0)	2m 1s
test (ubuntu-latest, 9.0, 1, 1, 0, 0, 0)	2m 11s
test (ubuntu-latest, 9.0, 1, 1, 0, 1, 0)	2m 22s
test (ubuntu-latest, 9.0, 1, 1, 1, 0, 0)	2m 11s
test (ubuntu-latest, 9.0, 1, 1, 1, 1, 0)	2m 13s
test (ubuntu-latest, 16.0, 1, 0, 0, 0, 0)	2m 36s
test (ubuntu-latest, 16.0, 1, 0, 0, 1, 0)	2m 40s
test (ubuntu-latest, 16.0, 1, 0, 1, 0, 0)	2m 33s
test (ubuntu-latest, 16.0, 1, 0, 1, 1, 0)	2m 36s
test (ubuntu-latest, 16.0, 1, 1, 0, 0, 0)	3m 4s
test (ubuntu-latest, 16.0, 1, 1, 0, 1, 0)	2m 57s
test (ubuntu-latest, 16.0, 1, 1, 1, 0, 0)	3m 13s
test (ubuntu-latest, 16.0, 1, 1, 1, 1, 0)	3m 7s
test (ubuntu-latest, 16.0, 0, 0, 1)	1m 46s
test (macos-12, 9.0, 0, 0, 0)	1m 58s
success	1s
	47m 28s

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