Add autosectionlabel_full_reference configuration variable

[andrewjmaguire]

Is your feature request related to a problem? Please describe.
The autosectionlabel extension is useful but the use of just the current section title as the reference will not be unique when a document contains many same-named subsections as can be common in a large document.

Describe the solution you'd like
Add a variable that can make usable and uniquely named refs for subsection titles that are not unique.

Describe alternatives you've considered
None.