Add a function for computing a Clenshaw-Curtis quadrature.

Function clencurt(n1) takes the number of desired quadrature
points and returns a tuple (x,w) containing points and weights
for Clenshaw-Curtis quadrature over (-1,1).

Code courtesy of Dr. Greg von Winckel
http://www.scientificpython.net
Add a Clenshaw-Curtis quadrature routine.

In quadrature.py, add a function for performing Clenshaw-Curtis
quadrature. Add associated unit test in test_quadrature.py.

Code for computing Clenshaw-Curtis points and weights provided
by Dr. Greg von Winckel.
www.scientificpython.net