[WIP] added forecast.io node

added the forecast.io node. Looking for feedback/improvements
@knolleary I think it would make sense that as a next step, Ben could work on a Location (text, say Hursley, Hampshire) to coordinates node? Forecast.io takes coordinates only, however I think flexibility would be nice. Google has a relevant API: http://stackoverflow.com/questions/98449/how-to-convert-an-address-to-a-latitude-longitude