Lebesgue functions and some documentation

Add modifications to the Lebesgues function file. Now is possible to plot
the Lebesgues functions locally and globally(new). Also include some
modifications on FD_DivFreeMatrixStream.m to allow faster computations
(I'm still using symbolic toolbox though). Now the interpolants depend on
the coeffs explicitly.

Some documentation on both modified files was added via Matlab publish.

FUTURE updates:
Adapt testConvergenceDerivative.m to work with the new
FD_DivFreeMatrixStream.m.
Including RBF code

I'm adding some part of the RBF code. This should be good enough to create
functions and scripts like the lebesguefunction and
testConvergenceDerivative of the polynomial case.
Lebesgue and cardinal functions RBF case

Add the function for visualizing the Lebesgue function and cardinal
functions for the divergence-free RBF interpolant. Also, fix some scaling
issues on the plot of the cardinal functions for the RBF and polynomial
method.