add contemporaneous coupling effects

[milanwiedemann]

see Wang, L., Zhang, Z., & Estabrook, R. (2009). Longitudinal mediation analysis of training intervention effects. In S.-M. Chow, E. Ferrer, & F. Hsieh (Eds.), Statistical methods for modeling human dynamics: An interdisciplinary dialogue (1st ed.). New York, NY: Taylor & Francis.

[milanwiedemann]

done, now all coupling parameters can be specified as contemporaneous (con) or lagged