Add PEP 621 project metadata #179

Job	Run time
macos	1m 40s
musllinux (x86_64-unknown-linux-musl)	1m 25s
linux (x86_64)	1m 48s
linux-cross (aarch64)	2m 25s
musllinux (i686-unknown-linux-musl)	1m 14s
linux (i686)	2m 30s
linux-cross (armv7)	2m 37s
musllinux-cross (aarch64-unknown-linux-musl, aarch64)	2m 7s
linux-cross (s390x)	2m 24s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	1m 44s
linux-cross (ppc64le)	2m 19s
sdist	14s
windows (x64)	2m 4s
linux-cross (ppc64)	2m 17s
windows (x86)	1m 59s
Release	0s
	28m 47s

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