Improve Euler_compare.ipynb based on suggestions from @rjleveque.
Improve Euler_compare.ipynb based on suggestions from @rjleveque.

Use exact solution for Sod shocktube.
Add titles to plots.
Remove unused ql, qr arguments to blastwave function.
Rename some variables to be more meaningful.

maojrs/riemann_book,maojrs/riemann_book,maojrs/riemann_book