tlwh in STrack should be tlhw

[mrtj]

STrack object should be initialized with an argument that is called tlwh. This acronym is commonly resolved as "top-left-width-height" format of bounding boxes. But the implementation of the bounding box conversation functions of STrack use this acronym as the coordinates were in "top-left-height-width" order. We should either change the acronym or the implementation.