Rename for clarity in preparation for further refactoring. Remove the need for `_nr` in function names. - Rename *_find() functions to *_exists() since they returned a boolean. - Rename *_find_nr() functions to *_find(). - Rename *_struct_elem_* to *_struct_member_*. - Rename DNA_elem_size_nr -> DNA_struct_member_size. - Rename DNA_elem_offset -> DNA_struct_member_offset_by_name.