paste in code for continent_size
completed 10.2 "sorting"
completed 10.3 "shuffle"
completed 10.4 "english number"
completed 10.5 "Wedding number"
completed 10.5 “Ninety-nine Bottles of Beer on the Wall.”
completed 11.8 "safer picture downloading"
completed 11.8 "Build your playlist"
completed 11.8 "refactor build_playlist"
completed 11.8 "final build_playlist"
completed 11.8 "final random playlist"
completed 12.2 "one billion seconds old"
move to chapter_12
completed 12.2 "Happy Birthday"
move to chapter_12
completed 12.6 "Party likes its roman_to_integer"
second version, much more efficient
completed 12.6 "Birthday Helper!"
fix 900
completed 13.2 "extending classes"