This introduces two new standard options for comments:


severity is a severity indicator, as provided by the tool. This can

  be used to help differentiate between errors, stylistic issues, or any

  other criteria offered by a tool.


text_extra is a list of tuples, each in (Header, Value) form.

  These are used for adding custom tool-specific information at the end

  of the comment text, after any built-in ones like Severity,

Column, or Error code.

Unit tests passed.
Used these in an upcoming change.