fixed a problem with p = 1, N = 4 kernel wrappers. added back in convergence. implemented L2 error.
new mesh generator. the code only needs to read the mesh at runtime; no more creating it every time you run. also, the mesh creator (genmesh.ph) will sort the sides so that all the boundary elements are first, inflow elements are second, and outflow elements are third to help avoid warp divergence.