Resumption of uploads

[konklone]

Resumption is likely to become a necessity for very large blobs in many use cases. To start off discussion, what about:

store.resumeWriteStream(resume_opts, opts, cb)

Where resume_opts are the options specifically needed to identify what and how to resume a write?

I could see something similar for resuming from a read stream, though maybe range requests are the right way to handle that, I'm not sure.

[max-mapper]

for inspiration: https://cloud.google.com/storage/docs/concepts-techniques#resumable

[konklone]

and for reference, I implemented this in s3-upload-stream: nathanpeck/s3-upload-stream#25