Add the inverse stereographic projection concatenated with a two-fold cover

This creates a field with topological charge 2.

src/inverse-stereographic-projection.py

@@ -2,6 +2,9 @@
 def f(x):
     normSquared = x[0]*x[0]+x[1]*x[1]
     return [2*x[0] / (normSquared+1), 2*x[1] / (normSquared+1), (normSquared-1)/ (normSquared+1)]
+    #a = 20
+    #normSquared = a*a*(x[0]*x[0]+x[1]*x[1])
+    #return [a*2*x[0] / (normSquared+1), a*2*x[1] / (normSquared+1), (normSquared-1)/ (normSquared+1)]
 
 def df(x):
     normSquared = x[0]*x[0]+x[1]*x[1]