Move references from combinat/ to references/index.rst

[hensc]

This is part of #27497.

One should also add DOI to all these references.

The attached file is the output from command grep -R "\.\.[ ]* \[" src/sage/combinat and then deleting a few false positives (thus it is an update of the file attached to #27497 after #28105).

Component: documentation

Issue created by migration from https://trac.sagemath.org/ticket/28445

[hensc]

Attachment: combinat.txt

[embray]

comment:1

Ticket retargeted after milestone closed

[mkoeppe]

comment:2

Batch modifying tickets that will likely not be ready for 9.1, based on a review of the ticket title, branch/review status, and last modification date.

[mkoeppe]

comment:4

Setting new milestone based on a cursory review of ticket status, priority, and last modification date.