Enable native/app address validation and conversion for wasm app (#102)

Enable setting external memory space for wasm app, the feature is disabled by default;
Remove wasm_application_exectue_* APIs from wasm_export.h which makes confused.

core/shared-lib/include/config.h

@@ -115,3 +115,13 @@
 #define APP_THREAD_STACK_SIZE_MAX (256 * 1024)
 #endif
 #endif
+
+/* External memory space provided by user,
+   but not wasm memory space and app heap space */
+#ifndef WASM_ENABLE_EXT_MEMORY_SPACE
+#define WASM_ENABLE_EXT_MEMORY_SPACE 0
+#endif
+
+/* Default base offset of external memory space */
+#define DEFAULT_EXT_MEM_BASE_OFFSET (-2 * BH_GB)
+