Be more systematic about using "@." (not ".") at end of sentence that
ends in a capital letter, and about appending "@:" after non-ends of
sentences that end in a lower case letter followed by "." followed by
whitespace. Omit unnecessary use of "@:" and "@.". Similarly for "?"
and "!". Be more consistent about putting a comma after "i.e." and
"e.g."; this is the typical American style and it's easier to code in
Texinfo.
Fixes: debbugs:12973
