Fixed redirect with completion property not being called

These are currently failing

Stream Usage

Adding the possibility to receive the callback to a different queue for all responses

Fixed unmatching Serializer with testThatJSONResponseSerializerSucceedsWhenDataIsValidJSON

Feature - Override Closures with Completion

Adding the possibility to receive the callback to a thread different from the main one to all response methods.

- stringResponseSerializer on Testing JSONResponseSerializer

For more details, please refer to Issue #1095.

Fix - Retaining Custom Content Types

Minor spelling correction in readme

Correct the spelling of CocoaPods in README