Full deps and stack upgrade

This releases updates all dependencies, including semver-breaking changes, hence the major bump.

It is also redrafted as a native ESM, which works fine with Jest and should have no impact on codebases that use it (they should not need to be ESM-by-default themselves, according to my tests).

This also fixes #17 and all dependabot pending PRs.

Fixing deps and vulns

• [BREAKING] Updated all dependencies to the latest versions
• Addressed dependency vulnerabilities as per npm audit; should take care of dependabot alerts.

Config validation is more Jest-style now

Checking for settings now relies on Jest's usual validation systems and uses a more Jest-like error formatting on the output, with a link to the configuration documentation.

Initial public release

This is the first public release, now that the repo is within jest-community and has configured CI.