message: Add wasi_* C-API function changes in migration guide for 3.0.0
  `wasi_env_new` changed signature
  `wasi_get_imports` changed signature
  `wasi_env_set_memory` was added
  Closes
diff: @@ -13,6 +13,7 @@ and provide examples to make migrating to the new API as simple as possible.
  - [Differences](#differences)
  - [Managing imports](#managing-imports)
  - [Engines](#engines)
  + - [C-API changes](#c-api)
  ## Rationale for changes in 3.0.0
  @@ -171,6 +172,31 @@ let engine = EngineBuilder::new(compiler).set_features(Some(features));
  let store = Store::new(engine);
  ```
  +### C-API
  +
  +The WASM C-API hasn't changed. Some wasmer-specific functions have changed, that relate to setting up WASI environments.
  +
  +- `wasi_env_new` function changed input parameters to accommodate the new Store API, it now is:
  + ```C
  + struct wasi_env_t *wasi_env_new(wasm_store_t *store, struct wasi_config_t *config);
  + ```
  +- `wasi_get_imports` function changed input parameters to accommodate the new Store API, it now is:
  + ```c
  + bool wasi_get_imports(const wasm_store_t *_store,
  + struct wasi_env_t *wasi_env,
  + const wasm_module_t *module,
  + wasm_extern_vec_t *imports);
  + ```
  +- `wasi_env_set_memory` was added. It's necessary to set the `WasiEnv` memory by getting it from `Instance`s memory exports after its initialization. This must be performed in a specific order:
  + 1. Create WasiEnv
  + 2. Create Instance
  + 3. Get Instance Exports
  + 4. Find Memory from Instance Exports and store it to WasiEnv
  + The function's signature is:
  + ```c
  + void wasi_env_set_memory(struct wasi_env_t *env, const wasm_memory_t *memory);
  + ```
  +
  [examples]: https://docs.wasmer.io/integrations/examples
  [wasmer]: https://crates.io/crates/wasmer
  [wasmer-wasi]: https://crates.io/crates/wasmer-wasi
  