[Issue #1177] Adding upload/download progress callback setters for individual tasks
Adding AFHTTPClient+Rocket
Bringing along the session headers for requests
Merge pull request #1185 from kcharwood/2.0_session_headers

[2.0] Bringing along the session headers for requests
Fixing implementation of request operation errors

Minor reformatting & refactoring
Removing backwards-compatible _AFNETWORKING_ALLOW_INVALID_SSL_CERTIFICATES_ check
Removing unnecessary inline comment
Updating documentation for allowsInvalidSSLCertificate property
Don't automatically inflate images larger than 1024 * 1024 in order to prevent memory issues.