info/retreat info/lretreat: Fix and clean up

info/retreat info/lretreat: Fix and clean up

.SY claims all arguments are individually optional.  Fix that, and
clarify that omitting the optional arguments shows current orders.

Don't complicate syntax with <SECTS>, <SHIP/FLEET> covers sectors.

The two pages are identical apart from header and footer.  They
mention land units briefly, then explain ship retreat.  Lazy.  Drop
the land unit mention from "info retreat", and rewrite "info lretreat"
for land units.

Update example output for current code.

Don't shout retreat conditions.  We've always accepted both lower and
upper case conditions.  Help has been advertising lower case since
commit bb5dfd8, v4.3.16.

While there, fix a few misspellings and such.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>