Exit on unknown options

Update a few dependencies, include minor refactorings, renamings and style changes, but in the main place:

• This version requires Node v14 or higher. Node v12 won't work with release 2.x any more.
• This version now exits on unknown options.

Before, my idea was to just print out a warning, but as @johnthagen mentioned, this would often remain unnoticed, so I changed it to be handled like an error. I hope that everyone is fine with this potentially breaking change.

Full Changelog: v1.2.2...v2.0.0