Coupled lattice analysis #60

This would complement the current MATRIX_Lattice class, which computes parameters for uncoupled lattices. Unlike the 2D case, there are multiple parameterizations of the 4D or 6D transfer matrix, so it would make sense to support these different parameterizations. Options include Lebedev-Bogacz [1], Edwards-Teng [2], Wolski [3], and Qin-Davidson [4]. Some of these apply also to non-periodic lattices.

Some work to this end is here, which analyzes the one-turn transfer matrix in the Lebedev-Bogacz framework. I did not implement tracking of the parameters throughout the lattice. I'm not sure if this is the best way to include these parameterizations.

[1] Lebedev, Valeri A., and S. A. Bogacz. "Betatron motion with coupling of horizontal and vertical degrees of freedom." Journal of Instrumentation 5.10 (2010): P10010. (https://arxiv.org/pdf/1207.5526)

[2] Edwards, D. A., and L. C. Teng. "Parametrization of linear coupled motion in periodic systems." IEEE Transactions on nuclear science 20.3 (1973): 885-888. (https://accelconf.web.cern.ch/p73/PDF/PAC1973_0885.pdf)

[3] Wolski, Andrzej. "Alternative approach to general coupled linear optics." Physical Review Special Topics—Accelerators and Beams 9.2 (2006): 024001. (https://journals.aps.org/prab/pdf/10.1103/PhysRevSTAB.9.024001)

[4] Qin, Hong, et al. "Analytical methods for describing charged particle dynamics in general focusing lattices using generalized Courant-Snyder theory." Physical Review Special Topics-Accelerators and Beams 17.4 (2014): 044001. (https://journals.aps.org/prab/pdf/10.1103/PhysRevSTAB.17.044001)