Remove unused figures
Two small typos in phugoid text.
Merge pull request #9 from FrenchKheldar/FK-fixes

Two small typos in phugoid text.
add note to find notebooks in wiki
add link to wiki
Fix lesson 2: removed extra m in Eq. (4)
Fix lesson 2—error in Euler scheme for phugoid eqs

The Delta t was in the wrong place for both equation (11) and (12).
Then these equations were repeated for no reason in the following
sub-heading.
Add linspace()->arange() challenge

and Pro tip to get the help pane
split cells to have headings in their own cell

plus add precision on convergence/consistency paragraph