Restore index of functions and commands in the manual
In the texinfo manual, there used to be an index for functions and commands (see https://www.dynare.org/manual/Command-and-Function-Index.html#Command-and-Function-Index).
This has been lost in the conversion to sphinx, and should therefore be restored.
By the way, if this is technically feasible, and index of variables (fields of
oo_, …) would also be useful.