DOC: config: fix alphabetical ordering of global section

the global section keywords were seriously misordered, and it's visible
that some mistakes have induced other ones over time, so it was about
time to fix this. Roughly 20% of the keywords were misplaced.

This commit only reordered the keywords index and their description,
nothing else was changed. It might be backported because it's a real
pain to find certain options there.
1 file changed