Add path to ProgressData

[marchuffnagle]

The sindresorhus/del-cli repository has a ticket to add a --verbose flag (sindresorhus/del-cli#24). That flag would show the names of files as they're deleted. There's a comment in that issue saying that the progress event from this package should be used for that feature. It looks like the progress callback was added in #141.

The onProgress callback of deleteAsync currently returns totalCount, deletedCount, and percent. To support printing out filenames as they're deleted, we would need to add path to that as well. Similar to what is done in sindresorhus/cpy, this would be the absolute path of the file that was deleted.

Because we need to handle the case where files.length === 0, the path property would be optional.