Begins implementation of Lafferty and Wyatt flux point method and API changes to flux_point.py

Adds xfail test command to added unit test
Add GaussianBand2D model
Add GaussianBand2D to docs
Improves flux_point API, adds lafferty method and unit tests and adds tutorial example
Makes some changes to the flux point tutorial to correct errors and improve clarity
Merge pull request #128 from ellisowen/flux_point_method

Flux point method
Fix broken docs link to gammfit classes
Fix a few PEP8 warnings
mutli gauss class, effective area class and irf info script