Add more people to AUTHORS

From a suggestion of Anders:

> Actually, since it’s probably best to keep them in an order that doesn’t
> change over time, here are the authors sorted by when their first commit
> was merged:

$ git log origin/master --pretty='%an' --topo-order --reverse | awk '{if (!h[$0]) {print $0; h[$0]=1}}'

I removed duplicates and most of the middle initials.
Fix spelling errors in AUTHORS (caught by ispell)