Tidy arguments, remove commented out code about pyfolio

[twiecki]

I think we should also remove passing in df_cum_rets and df_rets and just compute df_cum_rets, should not be a speed impairment.

[gusgordon]

Yeah, I was thinking about that too. I'll go ahead and do that.

[twiecki]

@gusgordon This is done, right?

[gusgordon]

Yeah. I think function call arguments have a standardized order at this point. The code structure is still a bit convoluted and varies in structure in some functions, but probably not worth worrying about at this point.