v2 Layout Refactoring

#11 merge

Reorganizes project layout to better match pandas-datareader. Creates submodules for API utilities, and top-level modules for grouping.

top level: by-functionality

• prosper.datareader.coins
• prosper.datareader.news
• prosper.datareader.stocks
• prosper.datareader.utils

lower level: by-API

• prosper.datareader.robinhood: Robinhood Stock Trading
• prosper.datareader.cryptocompare: CryptoCompare Coin Aggregation
• prosper.datareader.hitbtc: HitBTC Coin Aggregation
• prosper.datareader.iex: STUB IEX Stock Data

Deprecating Google feeds: finance.google sunsetted