Org Refile RFLOC and Struct Type

[Kevin Foley <kevin@kevinjfoley.me>]

I was recently working with `org-refile` and wanted to use a custom
target.  There is the `rfloc` argument which is documented as:

> RFLOC can be a refile location obtained in a different way.

There's no documentation as to how `rfloc` should be structured.  To
figure that out one has to read through the code which is made even more
difficult by the fact that the same argument is called `refloc` in
`org-refile--get-location`.

I plan to submit a patch to address this, however I wanted feedback on
whether using a struct type (cl-defstruct) could be an improvement
here before trying to implement it.

It seems using a defined structure would make both the documentation and
code more clear, however I rarely (if ever) have seen structures used in
the elisp code I'm familiar with.  Is there a downside to using struct
types that would make it a poor choice in this case?

Kevin