Moves from Signature V2 to Signature V4 for S3

[angerman]

This PR so far adds support for:

• [ ] S3.GetBucket (not yet tested)
• [ ] S3.GetBucketLocation (not yet tested)
• [ ] S3.PutBucket (not yet tested)
• [ ] S3.DeleteBucket (not yet tested)
• [ ] S3.GetService (not yet tested)
• [ ] S3.HeadObject (not yet tested)
• [x] S3.GetObject (REST)
• [x] S3.GetObject (URL)
• [x] S3.PutObject (without Content Sha256 by default)
• [ ] S3.Multipart (not yet tested)
• [ ] S3.CopyObject (not yet tested)
• [ ] S3.DeleteObject (not yet tested)
• [ ] S3.DeleteObjects (not yet tested)
• [ ] IAM Token (not yet tested)

It additionally does:

• [x] Reuse authorizationV4
• [x] Adds a pure version of authorizationV4
• [x] Extracted the Signature (signatureV4) and Credential (credentialV4) generation from the authorizationV4 as these were needed separately to support the URL generation for GetObject.

It also introduces a breaking API change, as Endpoints are replaced by Regions. I tried to keep these as similar to those provided in DynamoDb.

It should fix #167

[angerman]

Data.Bifunctor, was introduced in base-4.8.

[angerman]

Looks like I broke the google storage nearline example.

[angerman]

This might eventually break google storage support? I'm not certain about that, and I don't have a gcs account nor did I find detailed documentation on the S3 compatibility.

[aristidb]

To keep compatibility with Google, maybe put a SignatureVersion field into the S3Config? Then the google config can just say "V2 signing please".

[aristidb]

And do I understand it correctly that you consider your pull request complete and ready for merging when you have ticked off all the checkboxes, @angerman ?

[angerman]

I guess that would be optimal. Though I must admit, I don't see this getting finished soon. Especially multi-part seems to be quite tricky to get right.

[aristidb]

Superseded by #241