Fix Exports.swift

[gwynne]

This officially cleans up the last repo left that still has an uncorrected Exports.swift. Cleans up the README and CI workflows too.

[github-advanced-security[bot]]

This pull request sets up GitHub code scanning for this repository. Once the scans have completed and the checks have passed, the analysis results for this pull request branch will appear on this overview. Once you merge this pull request, the 'Security' tab will show more code scanning analysis results (for example, for the default branch). Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results. For more information about GitHub code scanning, check out the documentation.

[gwynne]

Note: Even though I've bumped the minimum Swift version requirement here, which is normally a semver-minor change, I'm leaving this PR marked no-release-required, on account of 5.6 was already effectively required by the dependency on Vapor, meaning no actual change has taken place aside from silencing the complaints of the 5.4 SwiftPM not knowing about DocC catalogs.

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (main@e6a147f). Click here to learn what that means. The diff coverage is n/a.

Additional details and impacted files

[](https://app.codecov.io/gh/vapor/leaf/pull/227?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) ```diff @@ Coverage Diff @@ ## main #227 +/- ## ======================================= Coverage ? 68.44% ======================================= Files ? 5 Lines ? 263 Branches ? 0 ======================================= Hits ? 180 Misses ? 83 Partials ? 0 ```