Grades

Class that implements a letter-based grading system (A+, A, A-, ...), and is able to naturally sort by the value of grade (i.e., A+ > A > A-).

Usage:
require "./lib/grade"

a_plus = Grade.new("A+")
a = Grade.new("A")
a_plus > a # should return true
[a_plus, a].sort # should return [a, a_plus]