Buffered Reader for Swift Driver

This change proposal introduces a buffering wrapper around image data for use
during image uploads. This wrapper helps improve the reliability of
image uploads by providing the ability to recover from errors occurring during
the upload process. The recovering ability comes from buffering the image
segments before uploading to swift. When an error occurs, Swift client resumes
the upload process from the last successful position determined using 'seek'
and 'tell' operations on the buffered image segment.