implement msize opcode

Signed-off-by: xermicus <cyrill@parity.io>

crates/integration/contracts/MSize.sol

@@ -0,0 +1,9 @@
+contract MSize {
+    uint[] public data;
+
+    function mSize() public pure returns (uint size) {
+        assembly {
+            size := msize()
+        }
+    }
+}