Added support for #max_item

Currently maxitem does not send back a valid JSON object and Faraday
explodes on a parsing error.  I do a manual get request in the request
class at the moment but this should be refactored the moment the API
updates or a better implementation can be put forward.
Updated readme and comments for max_item
Merge pull request #7 from allcentury/latest-max-id

Latest max