Support for custom headers on requests

[dkvasnicka]

Some AWS services use headers as a regular way of conveying the information on what you want AWS to do. A good example is S3, where the only way to select canned ACLs for objects is via headers: https://docs.aws.amazon.com/AmazonS3/latest/userguide/acl_overview.html#canned-acl

I searched this project thoroughly and found no official way of controlling outgoing headers. The only workaround I found was
#74 (comment) and it worked.

Would you consider adding this ability? If there is a way and I just overlooked it feel free to RTFM me :)