New S3 methods for fmsm objects

[mattwarkentin]

Hi @chjackson,

Would you be open to a pull request for a new predict.fmsm method for the predict S3 generic? I would generally match the argument signature to the predict.flexsurvreg method, where applicable.

The predict.fmsm method would wrap pmatrix.fs/pmatrix.simfs and totlos.fs/totlos.simfs. Thus, the prediction types could be: 'prob' and 'totlos'.

I would also be interested in adding a tidy.fmsm method that ostensibly does purrr::map_dfr(fmsm_obj, tidy, .id = 'trans').

What are your thoughts?

[chjackson]

Both of those sound good - thanks!

[kkmann]

@mattwarkentin would be interested in those too - you would not happen to have a PR lying around ;) ?