* Add CalendarImpl, DelegateCalendar, UnionCalendar * Add price_mid subscription service and dataframe service impl
0.1.8
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* Small bug-fix in business_day service
0.1.7
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* Change Calendar to have a simple is_business_day property and create the DetailedCalendar which knows about holidays and weekends. * Add business_days service
0.1.6
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* Small bug-fixes and updates to dependencies.
0.1.5
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* Fixes and convertion to poetry for project management