Module s3

this (incomplete) submodule contains convenient utility functions for interacting with an S3 storage.

• the implementation of AWS Signature Version 4 http headers generator was adapted from amazon's guide: https://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-header-based-auth.html
• and the implementation of AWS Signature Version 4 pre-signed url generator was adapted from this amazon guide: https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-param-auth.html