These functions add files in the R/ folder
that starts either with
fct_ (short for function)
The name of the file
If not NULL, the file will be module specific
in the naming (you don't need to add the leading
Path to the root of the package. Default is
Should the created file be opened?
Creates the directory if it doesn't exist, default is
should the module be created with tests?
The path to the file, invisibly.