Add support for the namespace

Add support for the namespace: the new designate initializer is `initWithHost:andPort:secure:withNamespace:` and accept an endpoint namespace (e.g. `@"/news"`).
I have also added a separate test suite for this feature.

I'd like your review and a confirmation before merge in the master branch? If it's ok after the merge we should create a new version and update the CocoaPods spec.