Extend derive(FromRow) with additional features/attributes

Handle #[sqlx(rename = "new_name")] on a struct field

Support the derive on a tuple struct and use by ordinal retrieval from the row

Handle #[sqlx(ordinal = 3)] to use ordinal retrieval from the row ( row.get(3) )

Handle a field that is impl FromRow. A parallel from serde_json would perhaps make this #[sqlx(flatten)].

#[derive(sqlx::FromRow)]
struct Bar {
    baz: i32  // row.get("baz")
 }

#[derive(sqlx::FromRow)]
struct Foo {
    foo: i32, // row.get("foo")
    #[sqlx(flatten)]
    bar: Bar
}