
Implemented headers:

 - [ ] autodiff_cost_function.h
 - [ ] autodiff_local_parameterization.h
 - [ ] c_api.h
 - [ ] ceres.h
 - [ ] conditioned_cost_function.h
 - [ ] cost_function.h
 - [ ] cost_function_to_functor.h
 - [ ] covariance.h
 - [ ] crs_matrix.h
 - [ ] dynamic_autodiff_cost_function.h
 - [ ] dynamic_numeric_diff_cost_function.h
 - [ ] gradient_checker.h
 - [X] gradient_problem.h
 - [ ] gradient_problem_solver.h
 - [ ] iteration_callback.h
 - [ ] jet.h
 - [ ] local_parameterization.h
 - [ ] loss_function.h
 - [ ] normal_prior.h
 - [ ] numeric_diff_cost_function.h
 - [ ] ordered_groups.h
 - [ ] problem.h
 - [ ] rotation.h
 - [ ] sized_cost_function.h
 - [ ] solver.h
 - [ ] types.h



Add todo list to src directory
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