Split constructor of Connection

This method was just to unwieldy.
This can be seen as a first step to introduce a Faraday Factory.
Extracted FaradayFactory from Connection

Also adjusted the Connection Spec
Extracted a spec for the FaradayFactory
Refactoring FaradayFactory
Remove need for NullLogger
Allow to add Request Middlewares
Allow to add additional response middlewares
Refactored FaradayFactory Spec
FaradayFactory refactored
Document the FaradayFactory
FaradayFactory Refactoring
Tiny style adjustments
Added the documentation of configuring middlewares to Connection
Added possibility to use `use` middlewares from Faraday
Rename blocky to a saner variable name in FaradayFactory spec
Constants for the default middlewares
Merge pull request #126 from triAGENS/tiny-refactorings

Split constructor of Connection
Updated change log for 0.12.0
Updated the README
Version 0.12.0 :shipit: