2.1 estat flags

I tried to use `readSDMX`on a Eurostat REST call. For this to succeed we need to pass in httpheader information (more specific: `list('User-Agent'='R')`. 

I added an argument to readSDMX that solves the problem though I am not sure if this is the right way to do this.

I also added an example that demonstrates the direct download from Eurostat.