Make order.rb and shipping_address.rb to take both symbol and string key for params.
Order.new now take basic param and shipping params; update order_xml_build.rb order_item.rb
due to walmart xsd changes; add first_name, last_name, phone field to shipping_address.
Update readme with new order param changes and order_item param changes.
Manual merge with master

Merge branch 'master' into order_params

Conflicts:
	lib/walmart_open/shipping_address.rb
	spec/walmart_open/order_spec.rb
	spec/walmart_open/shipping_address_spec.rb
Add accept string key param test cases to order_spec.rb and shipping_address_spec.rb
Update spec to improve readability.
Merge pull request #7 from xlu/order_params

Order param now take basic params and shipping params, updates made based on walmart xdd changes.