IOS

Note to iOS build

I used LLVM 4.0 to build ios-arm, ios-x86, and ios-x86_64. LLVM clang seems to have a bug in recognizing arm64, I used Xcode 9.0 to build ios-arm64 without -fopenmp. This is for build only, though. Since I have not built nd4j yet, it is to be decided later if MLPMnistSingleLayerExample and MLPMnistTwoLayerExample will run on iOS.