WIP Smlk invdyn

See merge request robotran/mbsysc!330

# Conflicts:
#   CHANGELOG.md
#   MBsysC/mbs_common/mbs_load_xml/mbs_load_libraries.h
#   MBsysC/mbs_common/mbs_module/mbs_aux.c
#   MBsysC/tests/cross_compilation/Dockerfile

```
Exception ignored in: <bound method MbsVtkOutputter.__del__ of <mbs_vtk.MbsVtkOutputter object at 0x7f3ba325b390>>
Traceback (most recent call last):
  File "mbsysc/MBsysC/build/python/mbs_vtk.py", line 127, in __del__
AttributeError: 'NoneType' object has no attribute 'MbsVtkOutputter_destroy'
```

Most of functions returns an error code

See merge request robotran/mbsysc!350

[Err msg][Ci-skip] updated header file and description

See merge request robotran/mbsysc!385

Merge branch 'MBsysPy_return_error' of https://git.immc.ucl.ac.be/robotran/mbsysc into MBsysPy_return_error

Small stuff

See merge request robotran/mbsysc!384

MBsysPy user vector are in resutls

Closes #242

See merge request robotran/mbsysc!383

[MBsysPy][BugFix][MbsDirdyn] Getting option resfilename was crashing if no name was specified by user.

Fix print user model vectors

Closes #229

See merge request robotran/mbsysc!381

Doc trajectories

See merge request robotran/mbsysc!382

[MBsysPy][ExtForce] user external forces are working even in C (symb)- Py (user) linking

See merge request robotran/mbsysc!380