Finalizin docs, API, error handlers for 1.0

[lainio]

• Finally! We are very happy, and thanks to all who have helped!
• Lots of documentation updates and cleanups for version 1.0.0
• Catch/Handle take unlimited amount error handler functions
  • allows building e.g. error handling middlewares/chains
  • this is major feature because it allows building helpers/add-ons
• automatic outputs aren't overwritten by given args, only with assert.Plain
• Minor API fixes to still simplify it:
  • remove exported vars, obsolete types and funcs from assert pkg
  • Result2.Def2() sets only Val2
• technical refactorings: variadic function calls only in API level