title: Change size of arrows using matplotlib quiver
body: <p>I am using quiver from matplotlib to plot a vectorial field. I would like to 
  change the size of the thickness of each arrow depending on 
  the number of data which produced a specific arrow of the vector field. Therefore 
  what I am looking for is not a general scale transformation of the arrow size, but the way 
  to customize the thickness of the arrow in quiver one-by-one. 
  Is it possible? Can you help me?</p>