made new getMagnification, theoryToObserved; include reduced shear as option from getShear
(#304)
added getLensing method for PowerSpectrum
(#304)
add getLensing for NFWHalo
(#304)
make new GSObject methods: applyLensing and createLensed
(#304)
fixed a keyword change that I missed
(#304)
fixed small issues with recent changes in functionality
(#304)
new unit test for various shear/magnification getters
(#304)
Merge branch '#304' of https://github.com/GalSim-developers/GalSim into #304