Adding documentation on CORS and JSONP

Fixes #144
Swapping out W3Schools link for MDN
Merge pull request #155 from socrata/cors-and-jsonp

Adding documentation on CORS and JSONP
Small grammar tweak to remove a repetition of "JSONP"
Grammar tweak to my grammar tweak...
added getting started with FME link
updated FME guide with fmwt and insrtructions for creating datasets
Switching from declared audiences in the header highlighting to path-based.
Adding sitemap.xml support because awesome.
Adding @mentions support
github.js is included globally now.
Fixes #157: Missing image
Adding a simple example of how to do data visualization with Python