Improve some descriptions of the configuration rules.

Improve some descriptions of the configuration rules.

The informal name for ISO-8859-15 is "Latin-9", capitalized;
use "US" instead of "USA" as an adjective;
consistenly speak of "Compose" instead of "Multi_Key";
use the same wording ("only") where the same thing is meant;
spell "semicolon" correctly;
use the "ShiftLock" word that is also used elsewhere;
don't hyphenate "Shift keys";
make a description more "descriptive" using third person;
remove inconsistent trailing periods;
Esperanto accents are not just circumflexes but also a breve; and
it are not the "accents" that are added but the "accented letters".

Signed-off-by: Benno Schulenberg <bensberg@justemail.net>