feat : add ViT operators

Context

This MR intends to add missing operators implementation to support ViT model inference:

• Erf
• MatMul
• Softmax

It handles issue #27 (moved)

Modified files

• MatMulImpl.hpp, MatMulImpl.cpp and Test_MatMulImpl.cpp, Add MatMul operator;
• ErfImpl.hpp, ErfImpl.cpp, ErfImpl_CUDA_kernels.hpp, ErfImpl_CUDA_kernels.cu and Test_ErfImpl.cpp, Add Erf operator;
• SoftmaxImpl.hpp, SoftmaxImpl.cpp and Test_SoftmaxImpl.cpp, Add Softmax operator;

TODO

• Erf
• MatMul
• Softmax