Some fixes to week 1

This changes little spelling/formatting errors. Changes the term "divider" to
the idiomatic English term "divisor". In addition, the text often uses the term
brackets to indicate "()" symbols. In North America, those are generally called
parantheses. "Brackets" usually means "[]". I have changed references to "()"
from brackets to parentheses in the text. All exercises and tests have been
verified to still pass with these changes.
Merge pull request #37 from mateor/master

Some fixes to week 1