Removed unused features & upgrade of workflows

What's Changed

• Add golangci lint by @EinKrebs in https://github.com/EinKrebs/json/pull/16
• Got rid of Decode and Encode by @EinKrebs in https://github.com/EinKrebs/json/pull/17

Full Changelog: EinKrebs/json@v0.2.3...v0.3.0