Updating the Json Engine to be less dependency heavy.

[ryanbartley]

Fix for #5.

• Updated Json Engine throughout to JsonCpp to loosen dependence tree.
• Updated CMake for OSX and Linux.
• Still needs update for Windows Visual Studio project.

[jtyjty99999]

@ryanbartley hi ， I use your fork under mac os, and compiled , when after cmake .., i type in make, then It has two error below:

`
[ 72%] Building CXX object IO-glTF/CMakeFiles/IO-glTF.dir/gltfWriter-Texture.cpp.o

[ 75%] Building CXX object IO-glTF/CMakeFiles/IO-glTF.dir/gltfWriter.cpp.o

/Users/adams/Documents/code/FBX-glTF/IO-glTF/gltfWriter.cpp:433:20: error:

  cannot increment value of type 'std::initializer_list<int>'

                            sIdentity4Mat[i++] = val;

                                          ~^

/Users/adams/Documents/code/FBX-glTF/IO-glTF/gltfWriter.cpp:597:8: error:

  cannot increment value of type 'std::initializer_list<int>'

                    ar[k++] = ((r [i] [j])) ;

                       ~^

2 errors generated.

make[2]: *** [IO-glTF/CMakeFiles/IO-glTF.dir/gltfWriter.cpp.o] Error 1

make[1]: *** [IO-glTF/CMakeFiles/IO-glTF.dir/all] Error 2

make: *** [all] Error 2`

I'm not family with c++, do you know how to solve this problem?

[jbaicoianu]

I had problems compiling due to the Casablanca dependency, this patch applied cleanly and I was able to convert a model with it. +1 for this patch!