Just a small erratum

Primarily this is a refactoring of Errata which is a large change, hence bumping the minor version number.

• Errata instances now have a error code and severity, not each annotation. This makes use much cleaner.
• Errata severity now has a very simple default, but can be overridden locally. This is more work but needed because places where Errata is used generally already have a defined level of severities and Errata should accommodate that.
• The error code is std::error_code for overall simplicity and compatibility.