fix import errors for builds w/o optional pem feature

[cpu]

In 0.11.2 the src/crl.rs and src/key_pair.rs modules were unconditionally importing crate::ENCODE_CONFIG, but this is only present when building with the optional pem feature. Additionally the crate example binaries, doc examples, and unit tests were often implicitly depending on pem, breaking compilation with --no-default-features.

This branch adds the correct import feature cfg gates, adds CI coverage for --no-default-features testing and clippy, fixes all of the various implicit pem dependencies, and updates CHANGELOG.md for a point release to include the fixes.

Resolves #161

[cpu]

ugh I think the merge queue isn't set up with the right branch protection rules. It merged before CI completed. I'll keep an eye on the actions run to make sure nothing broke.

[cpu]

I think the merge queue isn't set up with the right branch protection rules.

I've updated the branch protection rules to require all CI jobs except the coverage one. Administrative merge override still possible if circumstances demand it.

I'll keep an eye on the actions run to make sure nothing broke.

Edit: and it built all green.