Quadrature hankel transform + fixes
quadht.m:
- Implemented a Clenshaw-Curtis quadrature version 
of the hankel transform. Nodes and weights are 
generated using a fft method, allowing millions of
points to be simultaneously quadratures.
- The quadrature also gives an error estimate.

test_error.m:
- tests the error of the fdm against the analytical
solution, gives a relative error estimate.

Fixes:
- analy_green: moved the 1e-7 factor to the end of
the method.
- fdm_run: moved the 1e-7 factor after the fdm.

To do:
- Implement new version of the fdm