Multipart copy requires upload id, part number, and source range

[geofflane]

Trying to revive #106, which seemed to have gone dormant. The current implementation of upload_part_copy does not seem to work at all, and this fixes it.

This is a slightly different take. Like S3.upload_part, the upload_id, the part number, and the range are required attributes and shouldn't be put into opts, but part of the explicit API. Other than that, I copied the code mostly verbatim from #106 and just ensured it merged cleanly.

[geofflane]

This should fix #75 as well I believe.

[bernardd]

Hi @geofflane - thanks very much for the PR and apologies for taking so long to get to it. All looks good to me - usually I'd be concerned about changing the signature of an API function like this but looking at the docs, it really looks like you're absolutely right that there's no possible way it could have worked in its current form, so I've gotta assume nobody's using it :)