Added base Order class
Added base product class
Added spec_helper
Added order_spec
Added product_spec
Implemented Product class
Added test examples for the Product class
Implemented initialize and title tests
Finished implementing title test
Implemented price tests
Implemented category tests
Added Order class methods
Added Order test examples
Implemented initialize method of the Order class
Modified initialize method
Implemented initialize tests
Implemented filter_by_category method
Implemented filter_by_category test
Implemented add_product and get_product methods
Implemented add & retrieve tests