Modernize CI somewhat #271

Job	Run time
Verify code formatting	11s
Test on i686-unknown-linux-gnu (using cross)	1m 12s
coverage	39s
Check warnings	14s
Test on armv7-linux-androideabi (using cross)	1m 25s
Test on aarch64-unknown-linux-gnu (using cross)	1m 16s
Test Rust 1.60.0 on ubuntu-latest	2m 2s
Test on powerpc-unknown-linux-gnu (using cross)	1m 13s
Test Rust stable on ubuntu-latest	21s
Test Rust stable on macos-latest	22s
Test on powerpc64-unknown-linux-gnu (using cross)	1m 11s
Test Rust stable on windows-latest	48s
Test Rust stable-i686-msvc on windows-latest	1m 29s
Test Rust beta on ubuntu-latest	24s
Test Rust nightly on ubuntu-latest	23s
	13m 10s

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