Method text_raw

```rust use orgize::{Org, ast::Cloze}; let cloze = Org::parse("{{text}}").first_node:: ().unwrap(); assert_eq!(cloze.text_raw(), "text"); let cloze = Org::parse("{{$\\frac{1}{2}$}{}@id}").first_node:: ().unwrap(); assert_eq!(cloze.text_raw(), "$\\frac{1}{2}$"); let cloze = Org::parse("{{ [[file:my_image.png]] }{hint}}").first_node:: ().unwrap(); assert_eq!(cloze.text_raw(), " [[

(&self)