trytond-product-cost-history 6.0.0 Tryton module to historize product cost

The Product Cost History Tryton module adds a `Cost History` relate on the product form, showing the cost price evolution of the product. The history is based on the cost price stored on the incoming stock moves for goods and assets and based on the history table for service. When a historic cost price is needed, the value is taken from this history for goods and assets.