add_bias_force_comp

[Giulero]

This PR add the computation of the bias force of the floating-base dynamics equation.

[diegoferigo]

This PR looks good, even though I didn't check in details the calculation. I trust you (and the tests 😄).

The only minor comment is the value of the gravity acceleration. It would maybe useful to store it somewhere (like we did in blf). I saw you added a rw property, maybe the best pattern here since is something that does not change after setting it, is defining it in the constructor with a default value, similarly to this.

[Giulero]

Thanks @diegoferigo! :D

It would maybe useful to store it somewhere (like we did in blf)

Yes, it makes sense! I'll address this point in a separate PR.

is defining it in the constructor with a default value

I wanted to give the possibility to change the value also after instantiating the class, but, thinking about it, maybe its better to define it just in the constructor. Changing it!

[Giulero]

I use this PR also to add the copyright header. Merging!