Misc fixes

  
  - fix nbviewer link
  - missing "expeted" +links to hackpad (2013 and 2014)
  - link course an linear algebra
  - add IMathics demo notebook
  - nbviewer analytics figures
     - Raw/visit per month as a pseudo-table (you might want to remove) 
     - Average is now ~80 000 not 60
     - 1 Norvig = max 65 000 /day not 80 (100 in 2 days though, if you choose carefully the integration range)