Add method to cart instance to get count based on item quantity

[bezin]

Hello,

it would be nice to add a new method to the cart object to get the total number of items based on quantity, eg.

// Cart contains two items A and B, A with quantity 1, B with quantity 3

cart()->count() // Returns 2, because 2 items
cart()->countQuantity() // Return 4, because 1 A and 3 B

One could use this method to display the total number of items in cart in the page header.
Might be better added to ProductList rather than cart.

Cheerio