Pendulum simulation

[Ipuch]

• [x] 1. Joints with the grounds

• [x] 2. Forward dynamics with biomechanical model O(n3) see if (On) is easy to implement. https://youtu.be/tBGkfLL2Vs8

• [x] 2.2 Pendulum without forces

• [x] 3.1 external forces and torque applied on any point for any segment.

• [ ] 3.2 Internal generalized forces along joint axis (WIP)) #74

[Ipuch]

2.2 is completed :+1:

[Ipuch]

I believe 3.1 too.