update library according actual best practices

[thekip]

1. Building migrated to unbuild this stuff automatically discover entries in package.json and build cjs / esm / tsd target as well as checking common issues.
2. bin field added. cli also rewritten to typescript and included in building.
3. exports field added. It means lib explicitly states only allowed exports!
4. jest, typescript, eslint - updated
5. folder with generated artifacts deleted.
6. NodeJs bumped to v16. v14 has EOL in 1 month. Bumping version of nodejs requiring bumping a major version of package, so instead of two major releases in row in a short time, let's start from node16 right now.
7. GitHub Workflow for CI added. @MartinCerny-awin you need to add a codecov application to this repository, please read this guide the rest of the setup is already made.

Next steps - we need to resolve questions asked in #17 and i can continue working on setting up automatic releases with tags and changelogs in github.