Request to merge fixes to docca

From: Krystian Stasiowski (sdkrystian_at_[hidden])
Date: 2023-07-26 15:15:32

I would like to merge the following commits:

https://github.com/boostorg/docca/commit/0ce4e198398dbb52f1de0029f4ed9b7d2bded273
https://github.com/boostorg/docca/commit/8ba36c0c1e1adb32dbf4cd9c7f3cb36f339b8b8d
https://github.com/boostorg/docca/commit/4b61682742d6fc0d373698d4263502408816006a

To address these issues:
https://github.com/boostorg/docca/issues/136
https://github.com/boostorg/docca/issues/105

These fix assorted compatibility issues with doxygen 1.8.16 and newer