Get inspiration from other libraries

[HugoFara]

A nice mechanism library is gabemorris12/mechanism. Its provides many feature missing here, as it is intended for further mechanical analysis. Without copying it's content, here are three nice feature that can be added to pylinkage:

• Simple Chebychev–Grübler–Kutzbach criterion (already in pylinkage, but a simpler re implementation is better)
• Cam/Gear definition: I did not think about it, and it would be very nice to have it.
• Individual position/speed/acceleration for joints. Nothing hard here, but an implementation out-of-the-box would be great.