Battle simulator for Risk Europe

• risk_simulator_gui.py: This is the launcher.
• RiskSimGui.py: This is the class for a Tk GUI used to build the interface.
• RiskArmy: This is a class representing a Risk Europe army.
• simulation.py: This is a collection of functions used to simulate the battles.

• Properly handle exceptions when a non-integer is provided.
• Handle corner case when there is a tie in the combat (i.e. artillery killing eachother before proceding to further rounds).
• Properly handle the error when no value is given at all in some field (should default to 0).