wb.download country: add option to exclude aggregates

[data-coder]

It would be nice if we could pass an option to wb.download country to exclude aggregates. When using 'all' I'm also getting aggregates data like 'Word' and 'Euro area'.

wb.get_countries()['region'].unique()
array(['Latin America & Caribbean ', 'South Asia', 'Aggregates',
       'Sub-Saharan Africa ', 'Europe & Central Asia',
       'Middle East & North Africa', 'East Asia & Pacific',
       'North America'], dtype=object)

Or pease let me know if this is already implemented. I took a loot at https://github.com/pydata/pandas-datareader/blob/master/pandas_datareader/wb.py but coudn't find it.

[MaxGhenis]

My workaround is to take Afghanistan on, since the regions are at the top. It'd be great to avoid this!

raw = wb.download(indicator='SP.POP.TOTL',
                  country='all', start=2016, 
                  end=2016).reset_index()
first_non_agg_ix = raw.index[raw.country == 'Afghanistan'].tolist()[0]
dat = raw.iloc[first_non_agg_ix:]