Fix typos, punctuation, and unclear phrasing

Some of these changes are minor, such as adding semi-colon where
appropriate and deleting or rearranging words.

Others are more significant, such as correcting the name of
Edward Snowden and rewriting unclear phrases.

Hopefully, these changes are reasonable in most dialects of English, and
not just American English (my native tongue). =)

P.S. I enjoyed the book, by the way. Looking forward to the next one!