[Qemu-block] Incremental Backup Wiki

[John Snow]

Updated the article's "Development & Status" section with a summary:
http://wiki.qemu.org/Features/IncrementalBackup#Development_.26_Status

Please revise and comment as you see fit for planning reasons. I don't
want to put words in anybody's mouth, so please correct me if I have
misrepresented anybody's intentions, use cases, design goals, etc.

The biggest mystery at the moment appears to be how we intend to handle
the external backup API. The rest appears to hinge mostly on reviews.

Thanks,
--js