[Dependencies] Update Athena-Core (1.3.0), Athena-Entities (1.2.2), FreeType (2.4.9) and add rapidjson (0.11.0)
Switch from a multiple-file configuration system to a JSON-based one
Add functions to create a render window
Add the render system-related options in the the JSON-based configuration
Better redirection of the Ogre logs