Add list with explanations of editor messages

[MeAmAnUsername]

Summary
Add a list with explanations for errors, warnings and notes to the documentation

Todo

• Get list of all errors, warnings and notes
• Consolidate/merge messages where practical
• Create file, add to TOC
• Write list

Reason
While most errors, warnings and notes should be self explanatory, they often do not exhaustively explain everything, so it would be nice to have such an explanation in the documentation

Description
Messages can be consolidated/merged when practical. I expect that many Type mismatch messages can be merged.
Each message should explain what it means, the cause, and how to solve it.
Also explain what BUG: and BUG?: messages mean: a fundamental assumption of the DSL static semantics spec turns out to not be true, so it is (or for BUG?, might be) a bug in the spec. Please file a bug report.

Related issues
None