Fix #4: Allow to set maxAge and IoUThreshold

[lamhoangtung]

Fix #4: Allow to set maxAge and IoUThreshold like this:

sortnode.SortNode(kMinHits, kMaxAge, kIoUThreshold, kMinConfidence);

The SortNode object can be initialize with 4 arguments in the following order:

• kMinHits: (int) Minimum number of hits before a bounding box was assigned a new track ID (should be 3)
• kMaxAge: (int) Maximum number of frames to keep alive a track without associated detections
• kIoUThreshold: (float between 0 and 1) Minimum IOU for match (should be 0.3)
• kMinConfidence: (float between 0 and 1) Bouding boxes with confidence score less than this value will be ignored