Given a piece of stexi, return an index of a specified variety.
Note that currently, stexi-extract-index doesn’t differentiate
between different kinds of index entries. That’s a bug ;)
Given an stexi tree tree, index all of the entries of type
kind. kind can be one of the predefined texinfo indices
(concept, variable, function, key,
program, type) or one of the special symbols auto
or all. auto will scan the stext for a (printindex)
statement, and all will generate an index from all entries,
regardless of type.
The returned index is a list of pairs, the CAR of which is the entry (a string) and the CDR of which is a node name (a string).