Add sample code

New file matrix/matrix_gpu.cu
```
$ nnvcc matrix_cpu.cu
$ ./a.out
Processing time: 13 (sec)
```
New file matrix/matrix_cpu.cu
Need option ```-lcutil_x86_64```
```
$ nvcc matrix_gpu.cu -lcutil_x86_64
$ ./a.out
Processing time: 105.556999 (msec)

Press ENTER to exit...
```
13 (sec) -> 105.556999 (msec)
This is 1000 times!!!