rapidjson: rapidjson headers removed from public interface.
json: json writers removed.
utils: rapidjson_writer added.
config: configure() methods moved out from config structs.
config: ability to pass rapidjson::Value as config removed.
tests/CMake: add GTEST_TARGETS dependency only if Google Test is compiled from sources.
utils/rapidjson_writer: support rapidjson 'v1.0 Beta'.