The "Do Nothing" Release

* CHANGLOG tweaks.

* Moved CHANGELOG to CHANGELOG.md.
* Updated the development dependencies. Added a CHANGELOG.
* Update README.md
* Updated the dependencies.

Added a SignerInterface interface

Now you can type-hint against an interface-compatible class in your projects.

Fixing the stupid

Aside from documentation and README updates, the only actual issue this resolves is #3.

Big Bang

Initial release.

Based on a simplified version of the AWS Signature v4 implementation from the AWS SDK for PHP.