write BINARY VTK file for tetrahedral grid with scalar and vector data

I wrote this because the other VTK writing files on the file exchange either do not do binary format, or they could not do *both* the mesh and the point data in binary format. So I wrote this. You can easily modify it to write 2-D unstructured triangle meshes, for instance.
There is also a test script you can run. Note: you need another program to view the .vtk file, e.g. Paraview.