The main focuses of this PR is to develop the c++ code and its Python bindings for the state and control cost models. However there are other important contributions:
- Added unit-test code for the state cost
- createData is a nonpure virtual function for various abstractions.
- Renamed the cost empty files.
- Removed Eigen::Ref for all constructors, useless thing that added undesired extra code for bindings.
- Used the getter functions for retrieve information in Python.
- Increased the FDDP solver tolerance in the unit-test. This was not fully tested by me.
It tackles the issue #194 (closed).