Removing irrelevant headers
Implemented `toobusy` to gracefully handle an overload scenario with a `Retry-After: 60` HTTP header, updated README.md, fixes #52

Created `config.lag` to define acceptable lag before triggering a 503 response, updated `this.start()` & `this.log.exit()` to handle `toobusy`
Merge pull request #54 from avoidwork/edge

Minor changes