Clarify why we set the direction of newSegment in moveSnake

Closes #78
Merge pull request #80 from zspencer/78-clarify-lesson-7-direction-assignment

Clarify why we set the direction of newSegment in moveSnake
Extract drawableCollection in lesson 2
killing any existence of sean
Merge pull request #84 from railsbridge/kill_sean

killing any existence of sean

closes #59
Merge pull request #83 from zspencer/57-improve-clarity-around-arrays

Extract drawableObjects in lesson 2
Merge branch 'master' into add-syntax-highlighting