value iteration

this brings up the machinery and some basic examples (used in lecture) for running value iteration on a GridWorld, on the DoubleIntegrator and the Pendulum.  

It also adds a FunctionHandleVisualizer class, so that the simple examples (xcubed, double integrator, gridworld, etc), don't have to pollute the directory with multiple files just to have a visualizer.

Does it make sense for the convergence criteria to be an absolute value?