support import of options from JSON file + cleanup for https://github.com/KhronosGroup/glTF/issues/166
Removed submodule rapidjson
embed rapidjson including fix for clang / LLVM
new path for rapidjson
added a light KVC in JSON objects + introduce config file for converter
handle conversion in the bool case for JSONNumber
unifying mapping of uniqueIDs and JSONValue
https://github.com/KhronosGroup/glTF/issues/152
cleanup logs
https://github.com/KhronosGroup/glTF/issues/161
https://github.com/KhronosGroup/glTF/issues/147
https://github.com/KhronosGroup/glTF/issues/174