Split up long files

[elinw]

This file

https://github.com/ropensci/rrricanes/blob/main/R/fstadv.R

is too long to be manageable. Let's work to break it up in a coherent way. My suggestion would be to use the first part of the function names and put each one in separate files with informative names. For example all the tidy_ functions could go in a file called tidy.R.