Add ProPhoto RGB standard #350

Job	Run time
Quick check (beta)	2m 22s
Compile and test MSRV (ubuntu-latest)	9m 21s
Quick check (stable)	2m 21s
integration tests (ubuntu-latest)	28s
Compile and test MSRV (macos-latest)	7m 58s
Quick check (nightly)	2m 26s
integration tests (macos-latest)	32s
Compile and test MSRV (windows-latest)	16m 25s
integration tests (windows-latest)	2m 18s
Test #[no_std]	23s
Documentation	35s
Miri tests	4m 57s
ci	1s
	50m 7s

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