(doc): Remove use of mut in Document method receivers where possible
Description
This refactors the Document
API until only the .typeset()
method requires &mut self
as a receiver.
In doing so, I also refactored the accumulation of warnings to be external to the Document struct.
Checklist
-
You have read, and followed the guidance in, the CONTRIBUTING guide -
The MR content has run through a pipeline, or at least has pipelines enabled. -
There are no licence concerns with this contribution (The README clearly states Subplot is MIT-0)