Derived the AwsSignatureV1 class from AwsSignatureV0 to alleviate code duplication. Note, both V0 and V1 could derived from a common V1/V2-specific abstract base class, but that really would be overkill, and historically, V1 was derived from V0 anyway.
Small code layout tweak for consistency.
Added AwsAbstractSignature::version implementaton tests.
Removed a dev-only @todo, which also happened to be interfering with doxygen.
A small tweak to allow doxygen to not warn about an internal, yet protected (and therefore publically visible) constructor.