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