Added subtract_business_days function.
Added subtract_business_days function.

Southpaw-TACTIC/TACTIC,Southpaw-TACTIC/TACTIC,Southpaw-TACTIC/TACTIC,diegocortassa/TACTIC,Southpaw-TACTIC/TACTIC,diegocortassa/TACTIC,Southpaw-TACTIC/TACTIC,Southpaw-TACTIC/TACTIC,diegocortassa/TACTIC,diegocortassa/TACTIC,diegocortassa/TACTIC,diegocortassa/TACTIC