Latest versions of Sphinx (at least 3.1.0) do not need the `*` escaped and
will render the `\` in the output if it is there, so remove it.
Fixes issue #6209.
This enables warnings as errors and fixes all current errors, namely:
- reference to terms in the glossary must now be explicit (:term:)
- method overloads must not be declared as a separate method or must
use :noindex:
- 2 cases where `` should have been used instead of `