Oblique shock instead of cone shock

[dug20]

Currently assumes an oblique shock (i.e. 2D shock for a wedge) in front of the tangent ogive nosecone, but I think that's not technically correct and it would be better to assume a 3D cone shock.

[dug20]

Some examples of cone shock solvers made by others:

https://github.com/Davide-sd/pygasflow

https://gist.github.com/gusgordon/3fa0a80e767a34ffb8b112c8630c5484