message: Simplify root doc comment code example
  Use `#` doc comment feature to hide some unnecessary codes which are required but not useful for readers.
diff: //! ## Examples
  //!
  //! ```
  -//! #[cfg(feature = "sled-storage")]
  -//! fn main() {
  +//! # #[cfg(feature = "sled-storage")]
  +//! # fn main() {
  //! use gluesql::prelude::*;
  //!
  //! let storage = SledStorage::new("data/doc-db").unwrap();
  //! let output = glue.execute(sql).unwrap();
  //! println!("{:?}", output)
  //! }
  -//! }
  +//! # }
  //!
  -//! #[cfg(not(feature = "sled-storage"))]
  -//! fn main() {}
  +//! # #[cfg(not(feature = "sled-storage"))]
  +//! # fn main() {}
  //! ```
  //!
  //! ## Custom Storage
  