Update kspace documentation

[Eric Harper]

Could you please update the docstring documentation?

[Eric Harper]

@jens_glaser since it looks like you have added code most recently, could you please go through and update the documentation and add it to the sphinx build files since there's both cython and python kspace modules? You can use the branch UpdateDocumentation

[Jens Glaser]

I will have a look after AICHE

[Eric Harper]

@jens_glaser could you please take a look through the documentation (currently in the branch AddCiteFunctions).

[Bradley Dice]

Merging into #50.