Instead of just renaming it, I reconsidered what the API should look
like. A custom separator for author does not make sense positionally
but accepting a name, and defaulting it, does fit with what someone
would expect.
I removed the `_from_crate` suffix because it doesn't seem necessary.
We don't have this kind of naming for the derive. I feel it cleans
things up this way.
This is prep for moving the derive tests. Besides organizing the test
folder for each API, this should reduce link time at the cost of
re-compiling more when a test changes.
