Port functions from mosaic to fetch

[rpruim]

I've brought over fetchData(), fetchGoogle(), and fetchGapminder() (and fetchGapminder1()).

Other things that could move include:

• read.file() -- this is not as custom, it's just a wrapper to smooth over differences in read.*()
• CIAdata() -- we use this in our map examples. If we get rid of it in mosaic, we need new examples for our mapping stuff or need to also put the mapping stuff elsewhere or else fetch will need to be at least in the Suggests for mosaic. The spirit of CIAdata() fits this package better (a fetcher from a remote repository of data). It could be renamed fetchCIA() or fetchFactbook().

Any other candidates?