cli: add support for encoding pointcloud sequences
This commit enables the codec to encapsulate more than one frame in the coded bitstream. The number of frames to encode is controlled by the frameCount option. Support is added to encode multiple source frames from separate ply files based on a template input file name. A printf-like "%d" directive acts as a placeholder for the current frame number. Decoding functions in a similar way with a each frame decoded from the bitstream being written to a separate ply file named according to a template pattern. The first frame number used for file I/O may be set using the firstFrameNum option.