message: add load_custom_syntaxes method to engarde::Raw
diff: +use std::path::Path;
  +
  #[derive(Default, Debug, Clone)]
  #[non_exhaustive]
  pub struct Raw {}
  @@ -7,6 +9,8 @@ impl Raw {
  Self {}
  }
  + pub fn load_custom_syntaxes(&mut self, _syntaxes_path: &Path) {}
  +
  pub fn has_theme(&self, _name: &str) -> bool {
  false
  }
  