message: Improved memory documentation
diff: +//! The webassembly::Memory() constructor creates a new Memory object which is
  +//! a structure that holds the raw bytes of memory accessed by a
  +//! webassembly::Instance.
  +//! A memory created by Rust or in WebAssembly code will be accessible and
  +//! mutable from both Rust and WebAssembly.
  use memmap::MmapMut;
  use std::fmt;
  use std::ops::{Deref, DerefMut};
  