BF - csd model is fitting coefficients instead of data

I believe there is a bug in the CSD code, it seems that we're fitting on spherical harmonic coefficients instead of the data in `csdeconv`. I've made a gist [here](https://gist.github.com/MrBago/9681461) which allows you to compare the results of fitting using the two approaches. The fix is pretty easy, but the documentation should also be update to reflect the fix. Also there are a few other functions in this module that might need a similar fix and we should write some tests for this. I don't have time to work on this any more tonight and I'd love some help if anyone feels like jumping in.