Added checks so customers not add a 0 value item to their cart.

Signed-off-by: Zane M. Kolnik <zanematthew@gmail.com>
Few bug fixes relating to subtotals and empty prices in cart.

Signed-off-by: Zane M. Kolnik <zanematthew@gmail.com>
Readme, version number update.

Signed-off-by: Zane M. Kolnik <zanematthew@gmail.com>