Added Chebyshev class and test

Chebyshev is an distribution between [-1, 1]. This implementation scales and shifts the interval to [0, 1].
Added Joukowski class and test

This is the camber line part.
Added Joukowski class and test

This is the thickness distribution part
Small performance and readability improvement

The return line in camberline.Joukowski.as_array and thicknessdistribution.Joukowski.as_array now evaluates around 20% faster.
Small performance improvement

Multiplying a numpy array with a scalar is faster then multiplying as scalar with a numpy array.
Merge pull request #1 from 4ndr345/master

Custom ignores