Include some sane defaults in all logging messages

The call to `replacePathParams` had to be moved down a few lines. At its previous position it could only replace tags in the path portion coming from the service client call. By moving it down it can now replace tags set in the base URL portion.
Unfortunately we don't have tests for the fields in the events, but could you update the docs? https://github.com/groupon/gofer/blob/master/API.md#start