This class is used for defining reward functions in grid worlds that are a function of cell of the world to which
the agent transitions. That is, a double matrix (called rewardMatrix) the size of the grid world is stored. In an agent transitions
to cell x,y, then they will receive the double value stored in rewardMatrix[x][y]. The rewards returned for transitioning to an agent position
may be set with the
#setReward(int,int,double) method.
This reward function is useful for simple grid worlds without any location objects or worlds for which the rewards are independent
of location objects. An alternative to this class is to define worlds with location objects and use the atLocation propositional function
and location types to define rewards.