Several updates, optimizations and fixes mainly related to automatic differentiation
This branch includes the following enhancements and fixes:
- automatic differentiation support for beam, rigid body, modal body, automatic structural, total joint and total pin joint
- fix compilation of parallel naive solver
- fix memory leaks in parallel naive solver
- fix missing derivatives update of modal node
- optimize dot product in sp_matrix_base.h
- add new unit tests in sp_gradient_test.cc
- add automatic differentiation support for constitutive laws
- fix double free in parsinc.cc
- fix invalid memory access in dataman.cc
Please let me know, if you want to apply only a subset of those changes. Then I can provide separate branches.