Add pre-processing for requests and responses.
Added missing interface file.
Make pre-processing work per request and accompanying response.
Remove wrong file.
Add pre- and post-processing for request and response.
Remove old file.
Sample for pre- and post-processing requests and responses.
Add a note about which thread calls pre- and post-processing methods.
Introduce an interface for adding arbitrary JSON objects.
Merge pull request #666 from fineswap/JsonValueInterface

Introduce an interface for adding arbitrary JSON objects.
Merge pull request #664 from fineswap/PrePostProcessing

Add pre-processing for requests and responses.
Merge pull request #665 from fineswap/PrePostProcessingSample

Sample for pre- and post-processing requests and responses.
Fixed missing String value in Samples, see fc745f8226b9d04effa10c5c68ee65b1b3f62a9c
Removing UTF8 BOM if the response is parsed and returned as String, Closes #659
Tested and statically set specific version of Android Gradle Plugin, for stability
Source formatting, curly brackets fixup