Ahodges/documentation/doc115

@JAAkana , @stroilova , @mhoeber @srpearce , I'd appreciate your comments on the new sections in this chapter. DOC-115.
@shnayder , this is a similar request to one you made for the student answer distribution report, which I will be working on next.
Also see http://draft-jaakana-edits.readthedocs.org/en/latest/running_course/course_grades.html