Bump version to 0.3.0 #432

Job	Run time
macos-x86_64	42s
macos-aarch64	25s
sdist	1m 38s
windows (x86_64-pc-windows-msvc, x64)	1m 23s
windows (i686-pc-windows-msvc, x86)	1m 23s
linux (x86_64-unknown-linux-gnu)	1m 25s
linux-arm (aarch64-unknown-linux-gnu, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	1m 25s
linux (i686-unknown-linux-gnu)	1m 25s
linux-powerpc (powerpc64le-unknown-linux-gnu, ppc64le)	1m 25s
linux-arm (armv7-unknown-linux-gnueabihf, armv7)	1m 24s
linux-powerpc (powerpc64-unknown-linux-gnu, ppc64)	1m 23s
linux-arm (arm-unknown-linux-musleabihf, arm)	1m 24s
linux-s390x (s390x-unknown-linux-gnu, s390x)	1m 24s
musllinux (x86_64-unknown-linux-musl)	1m 24s
musllinux-cross (aarch64-unknown-linux-musl, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	1m 24s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	1m 24s
musllinux-cross (powerpc64le-unknown-linux-musl, ppc64le, nightly)	1m 24s
musllinux (i686-unknown-linux-musl)	1m 24s
	23m 46s

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