New returns an S3 struct which wraps an S3 client using the default AWS credentials chain.

NewConcurrent returns an S3Concurrent client, which embeds an S3 client, and has a ConcurrencyManager to allow the use of the GetAllConcurrently function.

NewWithMaxRetries returns the same as New(), but with the back off set to up to maxRetries times.

NewWithOptions returns the same as New(), but with the additional option functions applied.