[Dev] Kepler add examples

Add examples:

- $L^1$-minimization [two-body problem](https://caillau.perso.math.cnrs.fr/research/sicon-2016.pdf).
- $L^1$-minimization [CR3BP](https://caillau.perso.math.cnrs.fr/research/cele-2012.pdf).
- [Minimum time, CR3BP](https://caillau.perso.math.cnrs.fr/research/sicon-2012.pdf).