* allow multiple definitions for headers "Set-Cookie" and "Link". 

* allow multiple definitions for headers "Set-Cookie" and "Link".
* Fix apiaryio/snowcrash#75


These header names should be a part of this [code](https://github.com/apiaryio/snowcrash/blob/137b2133727bab2936318b96730002a92f9fecec/src/HTTP.cc#L13) and then we should use them here somehow.