corrected minor typos

just some minor copy-and-paste issues I stepped over while reading
Merge pull request #18 from nobozo/master

Edits From Jon Forrest - Please Let Me Know If You Like These
Merge pull request #10 from albers/typo-fixes

corrected minor typos
Merge pull request #19 from nobozo/master

Yet more minor edits
Merge pull request #20 from nobozo/master

Probably the last of ch1-2 edits.