Switching from sqlite to mongodb, so updating setup.py version and dependencies.
Replaced sqlite to pymongo in symbols.py
Refactored symbols.py. Added unit tests.
Refactored symbols.py: functions moved to a class.
Removed schema and removed sqalchemy from dependencies.
Implemented insert_historical_prices and select_historical_prices
Added more tests for insert and update marketdata
Finished insert/select historical prices. renamed _id field to date.
Implemented symbols.last_date and unit tests
Updated update_marketdata and added unit tests
Refactored get_marketdata. Made all unit test successful.