Working Examples on GH, Events, and Api Doc

Fixed js and json pathing so examples work at http://esridc.github.io/cedar/

Added example to explore eventing http://esridc.github.io/cedar/examples/scatter-events.html
- currently using the native vega events 

Initial API docs http://esridc.github.io/cedar/api-reference/
- require formatting / styling

Changed "generateChart" method to "compile" - open to ideas on naming this method. http://esridc.github.io/cedar/api-reference/compile.html