Add more crate-level docs #92

Job	Run time
Cargo check	18s
Clippy lint checks	22s
Minimal dependency versions build	27s
Build & test (stable, macos-latest)	17s
Build & test (stable, ubuntu-latest)	24s
Build & test (stable, windows-latest)	1m 15s
Build & test (nightly, ubuntu-latest)	20s
Build & test (1.88, macos-latest)	22s
Build & test (1.88, ubuntu-latest)	24s
Build & test (nightly, macos-latest)	21s
Machete dependencies checks	1m 58s
Code formatting checks	20s
Build & test (1.88, windows-latest)	1m 2s
Build & test (nightly, windows-latest)	48s
Build with each feature combination	20s
Miri test	1m 0s
	9m 58s

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