Wip fix logger

`webmachine_perf_log_handler` would crash if when logging a non standard HTTP method. For example:

```
curl -XFOO http://localhost:8000
```

would crash the handler with `{badarg, [{erlang, atom_to_list, ["FOO"]}, ...`

This fixes it and also fixes the imprecise typing of the `wm_log_data` record