Split Signer into separate project

[rmmeans]

I'd like to request that this library be split into two parts, one for AWS signing and the other for S3 which would depend on signing requests. It is essentially just a split right down the package line that already exists.

The reason I'd like to see this is because we'd like to build a Play DynamoDB impl that doesn't require the use of the AWS SDK since it is blocking. We have already proven this works great when using the signer portion of this library - we'd just like to see it split into two parts and published to sonatype.

Thoughts?

[EECOLOR]

We had this setup previously: https://github.com/Rhinofly/play-aws-utils