scoringutils 2.0.0 pre-release issue

[nikosbosse]

• check function documentation is correct and clean
• check all relevant functions have input checks
• decide on pkgdown categories (Discussion: Which pkgdown function categories do we want to have?  #481)
• make sure the list of functions to export is exactly what we want. Some candidates for reconsideration:
  • merge_pred_and_obs()?
  • quantile_to_interval()?
    • ideally, we would like to not export it. I don't know how to do that given that it's an S3 method
  • run_safely()
  • validate_forecast_generic()
    • we're exporting it because people might need it when creating their own validation functions
• Rename and reorganise files #746