Added helper functions to allow integration w/ caching libraries

Hey, love the work you've done with this repo (I'm a total data geek and am excited to start working w/ Socrata).

I've broken the "get" request into its component parts: forming the json url, constructing the CURL request, and finally submitting it. Hopefully this will make it easier to integrate w/ disk caching libraries like PHP-SimpleCache that accept URLs as parameters.

-Matt