message: Update src/lib.rs comment, prepare v0.8 release
diff: //! "INSERT INTO Glue VALUES (200);",
  //! "SELECT * FROM Glue WHERE id > 100;",
  //! ];
  +//!
  //! for sql in sqls {
  //! let output = glue.execute(sql).unwrap();
  //! println!("{:?}", output)
  //! ## Custom Storage
  //! To get started, all you need to implement for `gluesql` is implementing three traits
  //! (two for functions, one running tests).
  -//! There are also three optional traits (`AlterTable`, `Index` and `IndexMut`),
  +//! There are also three optional traits (`AlterTable`, `Index`, `IndexMut`, and `Transaction`),
  //! whether implementing it or not is all up to you.
  //!
  //! ### Store traits
  //! * [Store](store/trait.Store.html)
  //! * [StoreMut](store/trait.StoreMut.html)
  //!
  -//! ### Store traits (optional)
  +//! ### Optional Store traits
  //! * [AlterTable](store/trait.AlterTable.html)
  //! * [Index](store/trait.Index.html)
  //! * [IndexMut](store/trait.IndexMut.html)
  +//! * [Transaction](store/trait.Transaction.html)
  //!
  //! ### Trait to run integration tests
  //! * [Tester](tests/trait.Tester.html)
  