Player: Add rotation and linear speeds, as well as their current state.
Player: Allow to move in the local coordinates and compute
world-speed equivalent.
Player: Update movement axis while rotating.
World: Add a function to advance a step.
Main: Handle key events, add world step in the main loop.
Rotation wasn't handled properly at all.
Properly bound between 0 and 360, and use
a proper modulo for floats.
Switch to float to have a more fluid rotation
between frames.
