Add `Cartoon` macros
Add a helper module Cartoon
that contains macros to generate expressions to compute
derivatives in axisymmetry and spherical symmetry using the cartoon and double cartoon approach.
I documented all formulae over at https://git.tpi.uni-jena.de/dg/notes.
I double checked the formulae against bamps
, so they should be correct.
Unitests would be nice, but I am too lazy atm.