Modernize CI somewhat #268

Job	Run time
Test Rust 1.60.0 on ubuntu-latest	1m 58s
coverage	45s
Test Rust stable on ubuntu-latest	25s
Check warnings	13s
Test on i686-unknown-linux-gnu (using cross)	1m 16s
Test Rust stable on macos-latest	22s
Test on armv7-linux-androideabi (using cross)	1m 30s
Verify code formatting	12s
Test Rust stable on windows-latest	42s
Test on aarch64-unknown-linux-gnu (using cross)	1m 15s
Test Rust stable-i686-msvc on windows-latest	1m 24s
Test on powerpc-unknown-linux-gnu (using cross)	1m 11s
Test Rust beta on ubuntu-latest	28s
Test on powerpc64-unknown-linux-gnu (using cross)	1m 13s
Test Rust nightly on ubuntu-latest	24s
	13m 18s

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