recreate shortcut for dt that keeps getting deleted
added section on Richardson extrapolation in 3rd lesson
Added discussion on Richardson extrapolation
Make text more precise when describing motion

especially when talking about the angles, we have pitch angle (positive
up), then glide angle in the force balance: a bit sloppy
turn around figure 3 for positive angle

and it's pitch angle, not glide angle
had to make a small change to reload fig

new figure not loading in nbviewer by simply replacing png file and
re-executing the markdown cell, yet git didn't detect a change in the
nb file?
minor change to line continuation suggestion
Merge pull request #10 from aitatanit/master

minor change to line continuation suggestion
change angle to gamma in force balance fig

there is still some confusion with angles in the text -- I updated the
figure showing forces to name the flight-path angle gamma (while
discussion above used theta for pitch angle, positive up!)
explain we follow Milne-Thompson/ centrifugal force

Derivation uses theta as positive upwards, and forces are in a rotating
frame, so we should properly speak of centrifugal force
checking a sign, executed style, no changes
Add new figure of forces on the glider

With trajectory pointing up, for a positive angle
Rewrote full-model formulation

Without magically eating constants like in the math notes. The factors
have physical significance!
Went through first two modules
Added gitignore for files inside lessons
removed pyc file
added corrections
Correct minor typos and grammar points.
Docstrings to numpydoc format.
Update the code to match the equations.

NOTE: should probably pick "real" numbers; currently chosen to match the original, non-dimensional equations.