Support Multipart Uploads/Downloads

[jmccann]

Seems on files greater then certain sizes a Multipart Upload/Download can be more performant. (15MB is when upload manager uses it)

Seems there are upload/download managers available to take advantage of this feature easily. It'll determine the when and handle it automatically.

References

• https://docs.aws.amazon.com/sdk-for-go/api/service/s3/
• https://docs.aws.amazon.com/AmazonS3/latest/dev/usingHLmpuPHP.html