[LPardue]

Editorial fixes from style review; one commit each:

• Simplify the methods sentence in Upload Creation
• Tidy the interrupted-request paragraphs
• Fix byte counts in Upload Creation example intros
• Clarify why Example D marks the upload complete
• Clarify when the client must not retrieve the offset
• Say a request "to" an upload resource
• Simplify where the append offset comes from
• Say "cancel the upload" in Upload Cancellation
• Name concurrent append or cancellation requests in parallel
• Make the Concurrency lock list parallel
• Label the Retry heuristics by status code