Clarify Section 7.3 * Acknowledge the fact that the context map is conceptually really a two-dimensional matrix with 2 different keys, but in reality stored as a one-dimensional array. * Mention that InverseMoveToFrontTransform will not cause the context map to have invalid indexes. This gives someone implementing a decoder sanity that they do not have to go through the context map again and check that all values are less than NTREES.