[Doc] added linear solver docu

Documentation/ProjectFile/linear_solver/c_linear_solver.md

Documentation/ProjectFile/linear_solver/eigen/i_eigen.md

...tion/ProjectFile/linear_solver/eigen/t_error_tolerance.md

...n/ProjectFile/linear_solver/eigen/t_max_iteration_step.md

...entation/ProjectFile/linear_solver/eigen/t_precon_type.md

...entation/ProjectFile/linear_solver/eigen/t_solver_type.md

Documentation/ProjectFile/linear_solver/petsc/i_petsc.md

...mentation/ProjectFile/linear_solver/petsc/t_parameters.md

Documentation/ProjectFile/linear_solver/petsc/t_prefix.md

Documentation/ProjectFile/linear_solver/t_lis.md

Documentation/ProjectFile/linear_solver/t_name.md