Major refactor of JSONify Posts
 - Split caching into separate functions
 - Re-wrote logic to fetch published posts only
 - Kept logic to update caching file on-the-fly
 - WIP: need to test Expires compatibility
Fix excerpt being blank

(apparently getting with id is deprecated so we have to setup global postdata to use it...)
Merge pull request #5 from unikent/develop

Major refactor of JSONify Posts