Added trapezoidal implicit integrator, with NR iterations and 2nd order accuracy. Tested. It works ok.
Added trapezoidal implicit integrator, with NR iterations and 2nd order accuracy.
Tested. It works ok.

andrewseidl/chrono,rserban/chrono,jcmadsen/chrono,hsu/chrono,andrewseidl/chrono,Milad-Rakhsha/chrono,projectchrono/chrono,dariomangoni/chrono,tjolsen/chrono,hsu/chrono,dariomangoni/chrono,rserban/chrono,hsu/chrono,dariomangoni/chrono,armanpazouki/chrono,rserban/chrono,amelmquist/chrono,PedroTrujilloV/chrono,Milad-Rakhsha/chrono,hsu/chrono,armanpazouki/chrono,armanpazouki/chrono,andrewseidl/chrono,projectchrono/chrono,Milad-Rakhsha/chrono,rserban/chrono,Milad-Rakhsha/chrono,PedroTrujilloV/chrono,Bryan-Peterson/chrono,armanpazouki/chrono,tjolsen/chrono,PedroTrujilloV/chrono,amelmquist/chrono,armanpazouki/chrono,hsu/chrono,rserban/chrono,projectchrono/chrono,jcmadsen/chrono,jcmadsen/chrono,projectchrono/chrono,Milad-Rakhsha/chrono,amelmquist/chrono,Bryan-Peterson/chrono,projectchrono/chrono,Bryan-Peterson/chrono,amelmquist/chrono,PedroTrujilloV/chrono,projectchrono/chrono,amelmquist/chrono,rserban/chrono,dariomangoni/chrono,Bryan-Peterson/chrono,dariomangoni/chrono,amelmquist/chrono,tjolsen/chrono,jcmadsen/chrono,Milad-Rakhsha/chrono,PedroTrujilloV/chrono,tjolsen/chrono,jcmadsen/chrono,dariomangoni/chrono,tjolsen/chrono,jcmadsen/chrono,jcmadsen/chrono,andrewseidl/chrono,andrewseidl/chrono,armanpazouki/chrono,rserban/chrono,Bryan-Peterson/chrono