Additional Collocation Factors

Currently Euler and Trapezoidal collocation factors are implemented. We may also desire Verlet and Semi-Implicit Euler Collocation factors, and to benchmark/compare/demo amongst the different methods.

See wikipedia's [verlet](https://en.wikipedia.org/wiki/Verlet_integration) and [semi-implicit euler](https://en.wikipedia.org/wiki/Semi-implicit_Euler_method), and Frank's [Hamiltonian colab notebook](https://colab.research.google.com/drive/1Kttq5w6Br39307qYj29CA_GAYAX0lU1-). Also see [this stack exchange](https://math.stackexchange.com/questions/1849304/are-s-i-euler-and-verlet-the-same-thing) about the difference between Verlet and Semi-implicit euler.