Create a bulk calculation function for multiple sites and specialties about nhsrwaitinglist

[jacgrout]

I think it might be possible to achieve this using similar techniques to what I have put in the comments for #23 with variadic functions (my new learning for today ! ) and with pmap from the {purr} package.

[jacgrout]

@ThomUK If you have been playing with some real data then I just wondered if you had done any work that solves this? If not I'm happy to give it a first go/look

[ThomUK]

I have something partially built. It would be good to think about the incoming data format. Do we prefer a single dataframe with a column for specialty, or a list in a dataframe for each specialty?

The initial version i have is a list, but I may try to convert to a flat dataframe.

I will push up my work so far to a branch this weekend...

[jacgrout]

I think this is closely linked to the pull request #63 for issue #23 which includes a bulk function to create synthetic data for multiple sites and specialties. It may result in changes being required to the structure of this data and consequently the functions, but its straightforward