🚀 Add a test that enforces clippy and rustfmt compliance

[dandavison]

Once the codebase is clippy-compliant, let's add a test that ensures it stays that way. (And the same for rustfmt). cc @MarcoIeni ref #380 #383

[MarcoIeni]

I know how to do it by using github actions. See this.
I don't know if you have plans to use them.

[dandavison]

I'm happy to switch to GitHub actions if that makes sense. But I'm thinking that's pretty much orthogonal to this issue since we can add shell commands here

delta/etc/ci/script.sh

Lines 10 to 15 in b149425

	cargo test --target "$TARGET" --verbose
	cargo build --release
	./tests/test_raw_output_matches_git_on_full_repo_history
	./tests/test_deprecated_options > /dev/null
	cargo run --target "$TARGET" -- < /dev/null

[MarcoIeni]

I'm happy to switch to GitHub actions if that makes sense.

I don't know, that's just what I happen to use for my open source projects, but yes, it's a separate issue.

Anyway, the commands should be the following:

cargo fmt --all -- --check
cargo clippy -- -D warnings

[dandavison]

Update: we've got a check for rustfmt, and a check for clippy commented out; the only remaining thing here is getting the codebase to pass clippy.

[dandavison]

Fixed at #422