Expanded the signing process to include AMZ headers and also correctly add Content-Type and Content-MD5 (if provided) to the authorization header
Merge branch 'master' of https://github.com/robertjpayne/AFAmazonS3Client into robertjpayne-master

Conflicts:
	AFAmazonS3Client/AFAmazonS3Client.m
[Issue #15] Refactoring request AWS canonical authorization header signing
Minor formatting
Adding region property

Refactoring baseURL calculation
Fixing analyzer warning for possible nil value of date in dictionary literal
Add key parameter unless added explicitly

Signed-off-by: Mattt Thompson <m@mattt.me>
Bumping version to 0.3.0
Add prefix header imports