Renamed is_neighbor to has_covalent_bond
Replaced boost::random by std::random in monte_carlo_task.cpp
Replaced boost::random by std::random in main.cpp
Renamed ligand_folder to input_folder
Marked ligand::write_models as const
Inlined ligand::get_atom_types
Enlarged the index width to 8, ligand stem width to 15, and progress width to 25. Output only the kcal/mol value of the top conformation