This commit removes all Signers except for the version 4 signer which is improved.

This signer now supports detailed test cases from the amazon documentation. These can be
used for communication with S3. The version is updated to 3.0.0 because this release is
not backwards compatible.
Merge pull request #2 from Rhinofly/Aws4SignerSpec

This commit removes all Signers except for the version 4 signer which is improved.