First commit for a 2D example
Updated the solution class to be a 2D approximation
Updated the Poisson class to be a 2D operation for the Laplacian w/ boundary conditions.
Updated the preconditioner to be applied to a 2D solution.
Updated the solver example program to make use of the 2D classes.
Changed the forcing function for the example so that a true solution can be calculated for the 2D problem.
Changed the way the iteration count is returned on successful completion from the GMRES routine.
Updated the preconditioner to simply use the diagonal entries of the second derivative matrix
Changed the way the number of restarts is calculated
Changed the preconditioner to be the diagonal entry of the Laplacian
Changed the preconditioner to just be the diagonal entries in the Laplacian. Also cleaned up the code in the preconditioner, updated the comments, and changed the name of the cholesky vector to diagonal.