Proposed improvements for Ch07

Fix typos, capitalize LINQ.
intro paragraph phrasing
paragraph spacing; removed single line breaks.
phrasing, plus a little humor
brevity
phrasing
pluralization
spacing
phrasing
spacing
startups -> start-upss
phrasing
tense and phrasing
pluralization
phrasing
phrasing
phrasing
word choice
phrasing
phrasing