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 "[]". The "{}" symbols are usually called
"curly braces". I have standardized those references to their general English counterparts.
 All exercises and tests have been verified to still pass with these changes.