text: Title: Subplot margins (Chapter 1, Exercise 2)
  Body: Hi @rougier,
  
  There is a statement about additional figure margins for Exercise 2 solution:
  https://github.com/rougier/scientific-visualization-book/blob/a6e0607fa8dbcfa5e6251cd7b64b5a094ad4e0f9/code/anatomy/inch-cm.py#L13-L15
  And there is a code that performs this adjustment:
  https://github.com/rougier/scientific-visualization-book/blob/a6e0607fa8dbcfa5e6251cd7b64b5a094ad4e0f9/code/anatomy/inch-cm.py#L27-L38
  It seems that in this case we need to have 0.125 inches margin on each side (not 0.25 as in the description), and `margin=0.25` (not 0.125 as in the code) because we multiply this margin by 0.5 when we call `plt.subplots_adjust()`.
  Is it correct?
  
  Thank you.