Fixing search/rewrite inside of block bodies

Should fix #72 with new tests. I'll post a followup PR to bump the version and update the changelog since this should be published ASAP.

There were a couple of problems but the gist is that we should unwrap `ExpressionStatement`'s since what we really want is the expression (not the statement). A better way to fix this may be to make `ExpressionStatement` and other expressions comparable (like we do with `Program`/`BlockStatement`). This works for now and I'll revisit during the rewrite as part of #64.