* [Py] User vector outputs are now available in the MbsDirdyn results field.

* [Py] Using C symbolic library and Python user is possible even with external forces.

* [Py] Adding missing fields in MbsData.

*[dirdyn][new option] A new option option called 'oneshot' is added.

-> It allows to compute the derivative function only once (no time derivation) at time = dt0.

-> See the 'flag_oneshot' in dirdyn options.

*[dirdyn][Fix] the function user_dirdyn_loop is now called only at the real time steps, even for multisteps integration methods.

*[dirdyn][Fix] the mbs_data->flag_stop is taken into account in all the integrators now, the simulation stops.

*[integrators][dirdyn] Add a new integrator called 'AlphaM' for alpha method. It is explicit, fixed step-size but with two stages and a bit smarter than Euler explicit :-)