wb.py needs a rewrite

[femtotrader]

Hello,

I think that all DataReaders are now objects except wb.py maybe this file need a rewrite.

see also #117

It should help to have cache support for World Bank #48

One possible API usage could be

import requests_cache
import datetime
session = requests_cache.CachedSession(cache_name='cache', backend='sqlite', expire_after=datetime.timedelta(days=60))
DataReaderObject("wb", session=session).search(string='gdp.*capi', field='name', case=False)
DataReaderObject("wb", session=session).get_indicators()

Kind regards