Add argparse and enable saving point coud as .npy files

[yuqli]

Simple changes include:

1. add argparse in the main function to take input and output paths
2. enable saving point cloud as .npy files
3. commented out visualization of point cloud so the code can run on a headless server
4. revise README.md to add usage

[yuqli]

The old code hangs for some cases when the mesh only contains 2D surfaces. Modify the while loop to break when points threshold grows too high.

[yuqli]

New changes today: add a timeout function with multiprocessing to handle ill cases