Add Sankey demo

[psychemedia]

I did a quick demo of an openspending powered Sankey diagram using rCharts.

The demo should be able to pull the Sankey files from a URL, eg using the dir path:
sankeyPlot$setLib('http://timelyportfolio.github.io/rCharts_d3_sankey')

but it failed to work for me for some reason.... so I popped the demo files from @timelyportfolio into the examples dir.

We'd need to check license conditions if it remains...

[mihi-tr]

Tony,

This is great- however R packages are very picky on beeing installed. can you check do

R CMD build r-openspending
cp ropenspending_0.1.tar.gz /tmp
cd /tmp
tar -xvzf ropenspending_0.1.tar.gz
R CMD check --as-cran ropenspending

and make sure no NOTEs, WARNINGs or ERRORs pop up?

If yes I can safely merge it and still commit to CRAN (they are very picky about this...)