Outline and early draft of Phugoid module.
Complete draft of 3 notebooks for phugoid module.
Have students program solutions in their own notebook.
Fix mistakes caught by @gforsyth.
Add CSS injection.
Resolve most of the issues raised by @gforsyth and @ianhawke in the Phugoid notebooks.
Update README.md
Update README.md
Break up code into smaller chunks and mark solution cells.
Merge remote-tracking branch 'origin/phugoid' into phugoid

* origin/phugoid:
  Update README.md
  Update README.md
Rearrange code to be closer to explanation

Move library imports up (before method), move time discretization up to
explanation.
Small change: delta t was already defined

Removed second definition.
Ignore checkpoint file
Changed gitignore

To catch all checkpoint files.
Add comments to initialization cell

And add short intro paragraph before this cell.
Adjust plot

Add labels and make default font size larger
Correct picture of glider coordinate system.
Clean up a few things in the Phugoid notebooks.
Change fonts and colors in the CSS.
Move solutions to separate files.