Add doctest to check rescaling for Legendre basis

Fix #83

Add doctest to check for rescaling of Legendre basis.
Rescaled coefficients still provide comparable and
accurate results in Legendre notebooks example.

The equations in the cahn_hilliard_simulation class
were also changed to meet PEP8 styling forms.
Fix broken Legendre polynomial test case

Address #83

The previous commit fixed the broken scaling for the Legendre
Polynomial bassis. However, the test case, which worked with the
broken scaling was not updated to work with the new (correct) scaling.
Furthermore the tests have been changed to explicitly calculate the
test comparison values by constructing the Legendre Polynomials in the
test.
Merge pull request #1 from wd15/issue83-LegendreScaling

Fix broken Legendre polynomial test case
Merge pull request #100 from davidbrough1/issue83-LegendreScaling

Add doctest to check rescaling for Legendre basis