Merge pull request #75 from rust-cross/external-subcommand #338

Job	Run time
Check	54s
MSRV	5m 34s
Clippy	3m 10s
Test Suite (ubuntu-latest, stable)	8m 1s
Test Suite (ubuntu-latest, nightly)	9m 30s
Rustfmt	8s
Test Suite (macos-latest, stable)	7m 43s
spellcheck	12s
Test Suite (macos-latest, nightly)	9m 1s
Test Suite (windows-latest, stable)	18m 31s
Test Suite (windows-latest, nightly)	18m 6s
	1h 20m 50s

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