Here follows (hopefully) much improved versions of the patches. I have
to admit, a lot of the "decisions" of the last one were just plain
sillyness, but I hope I've correctly formatted the documentation. I
rendered it and it looked correct to my eyes, but that's my own eyes.

Both commands now take a prefix argument to pick a specific file or
buffer, and otherwise default to the currently visited one.

Further comments would be appreciated!

Thanks,
Barra Ó Catháin.