Give examples showing different usage of create_mash_prior

[pcarbo]

@gaow Judging by the code it looks like there are three different ways to use create_mash_prior, corresponding to whether fitted_g, mixture_prior or sample_data are provided as input. Could you provide one example illustrating each of these usages?

[gaow]

@pcarbo I think this might be a good opportunity to rediscuss the interface. Currently you are right that there are different ways all in the same function: fitted_g extract the information from a mashr fit, mixture_prior takes in the mixture (an R list) as is, and with sample_data we will generate summary statistics to compute the mixture.

I will add examples as is, to this function. We can then determine if we want this one function to use different data types ...

[pcarbo]

@gaow Well, a simple alternative that might be more clear would be to have three functions instead of one. (You'd have to figure what to call these functions.)