message: Add proper description of MemoryView API
diff: @@ -117,9 +117,62 @@ env_mut.memory = Some(instance.exports.get_memory("memory"));
  env_mut.alloc_guest_memory = Some(instance.exports.get_typed_function("__alloc"));
  ```
  -### New `MemoryView` API
  +### New `MemoryView` API (preparation for shared memory)
  -Adding the new memory view API (and show how people can update from previous usage)
  +Reading from memory has slightly changed compared to 2.x:
  +
  +```rust
  +// 2.x
  +let memory = instance.exports.get_memory("mem")?;
  +println!("Memory size (pages) {:?}", memory.size());
  +println!("Memory size (bytes) {:?}", memory.data_size());
  +
  +let load = instance
  + .exports
  + .get_native_function::<(), (WasmPtr<u8, Array>, i32)>("load")?;
  +
  +let (ptr, length) = load.call(&mut store)?;
  +let str = ptr.get_utf8_string(memory, length as u32).unwrap();
  +println!("Memory contents: {:?}", str);
  +```
  +
  +```rust
  +// 3.x
  +let memory = instance.exports.get_memory("mem")?;
  +let memory_view = memory.view(&store);
  +println!("Memory size (pages) {:?}", memory_view.size());
  +println!("Memory size (bytes) {:?}", memory_view.data_size());
  +
  +let load: TypedFunction<(), (WasmPtr<u8>, i32)> =
  + instance.exports.get_typed_function(&mut store, "load")?;
  +
  +let (ptr, length) = load.call(&mut store)?;
  +let memory_view = memory.view(&store);
  +let str = ptr.read_utf8_string(&memory_view, length as u32).unwrap();
  +println!("Memory contents: {:?}", str);
  +```
  +
  +The reason for this change is that in the future this will enable
  +safely sharing memory across threads. The same thing goes for reading slices:
  +
  +```rust
  +// 2.x
  +let new_str = b"Hello, Wasmer!";
  +let values = ptr.deref(memory, 0, new_str.len() as u32).unwrap();
  +for i in 0..new_str.len() {
  + values[i].set(new_str[i]);
  +}
  +```
  +
  +```rust
  +// 3.x
  +let memory_view = memory.view(&store); // (can be reused)
  +let new_str = b"Hello, Wasmer!";
  +let values = ptr.slice(&memory_view, new_str.len() as u32).unwrap();
  +for i in 0..new_str.len() {
  + values.index(i as u64).write(new_str[i]).unwrap();
  +}
  +```
  ### Managing imports
  