Fix fit_lc() failure on numpy 1.8 and related docstrings

In normalize_data() which is used in fit_lc and plot_lc, there was
a call where a MagSystem object was being passed to Model.bandflux().
This is not supported in numpy 1.8 because object arrays are not
broadcastable in that numpy version.
add test for minwave/maxwave
add test for fit_lc()
prevent build from cythoning pyx files unnecessarily
add contributors for 0.4.1 release
document 0.4.1 changes