Update the documentation of the snapshot variables in the Python Console (#17291)
In the Developer's Guide, the Snapshot Variables paragraph is not up-to-date: three more snapshot variables are created when opening the console with NVDA+control+z, but are not documented: caretObj, caretPos and review.
Description of user facing changes
Updated the paragraph with these three variables.
Description of development approach
I have based the description on the docstring of the functions that are called to create these variables;
While at it, I have noticed that the .md.sub generated while compiling the dev guide was not ignored by Git, so I have added it to the .gitignore file.