Add test to measure size overhead (#8)

* Don't use parity-wasm directly

* Add test that output size over head of metering

tests/diff.rs

@@ -1,10 +1,9 @@
-use parity_wasm::elements;
 use std::{
 	fs,
 	io::{self, Read, Write},
 	path::{Path, PathBuf},
 };
-use wasm_instrument as instrument;
+use wasm_instrument::{self as instrument, parity_wasm::elements};
 use wasmparser::validate;
 
 fn slurp<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {