Add ProPhoto RGB standard #355

Job	Run time
Compile and test MSRV (ubuntu-latest)	8m 51s
Quick check (beta)	1m 59s
Compile and test MSRV (macos-latest)	6m 18s
integration tests (ubuntu-latest)	22s
Quick check (stable)	1m 52s
Miri tests	4m 22s
Compile and test MSRV (windows-latest)	12m 49s
integration tests (macos-latest)	24s
Quick check (nightly)	1m 58s
integration tests (windows-latest)	2m 51s
Test #[no_std]	20s
Documentation	22s
ci	1s
	42m 29s

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