In-app Billing sample

This sample is provided to demonstrate Google Play In-app Billing. To read
more visit https://developer.android.com/google/play/billing/index.html

This game is a simple "driving" game where the player can buy gas
and drive. The car has a tank which stores gas. When the player purchases
gas, the tank fills up (1/4 tank at a time). When the player drives, the gas
in the tank diminishes (also 1/4 tank at a time).

The user can also purchase a "premium upgrade" that gives them a red car
instead of the standard blue one (exciting!).

The user can also purchase a subscription ("infinite gas") that allows them
to drive without using up any gas while that subscription is active. The
subscription can either be purchased monthly or yearly.