Implement native function pointer check, addr conversion and register, update documents (#185)

Modified WASM runtime API:
- wasm_runtime_module_malloc()
- wasm_runtime_lookup_function()
Introduced runtime API
- wasm_runtime_register_natives()

core/iwasm/common/wasm_exec_env.c

@@ -20,6 +20,14 @@ wasm_exec_env_create(struct WASMModuleInstanceCommon *module_inst,
         return NULL;
 
     memset(exec_env, 0, (uint32)total_size);
+
+#if WASM_ENABLE_AOT != 0
+    if (!(exec_env->argv_buf = wasm_malloc(sizeof(uint32) * 64))) {
+        wasm_free(exec_env);
+        return NULL;
+    }
+#endif
+
     exec_env->module_inst = module_inst;
     exec_env->wasm_stack_size = stack_size;
     exec_env->wasm_stack.s.top_boundary =
@@ -31,6 +39,9 @@ wasm_exec_env_create(struct WASMModuleInstanceCommon *module_inst,
 void
 wasm_exec_env_destroy(WASMExecEnv *exec_env)
 {
+#if WASM_ENABLE_AOT != 0
+    wasm_free(exec_env->argv_buf);
+#endif
     wasm_free(exec_env);
 }