Implemented addGasPump, getGasPumps, setPrice and getPrice of class GasStationImpl. Added unit tests for these methods.
Added additional unit tests for GasStationImpl.
Added naive implementation for buyGas and remaining getter/setter of GasStationImpl.
Restructured GasStationImpl to be thread-safe. Added some unit tests.
Cleanup and documentation for GasStationImpl.