Introduce `SmtProof` #977

Job	Run time
rustfmt nightly on ubuntu	11s
Verify the docs on stable	37s
build stable no-std for wasm32-unknown-unknown	16s
clippy nightly on ubuntu	45s
build nightly no-std for wasm32-unknown-unknown	26s
test stable on ubuntu with --features default,serde	41s
test stable on ubuntu with --no-default-features	43s
test nightly on ubuntu with --features default,serde	50s
test nightly on ubuntu with --no-default-features	50s
	5m 19s

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