Implement moving the player

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.

World.cpp

@@ -243,4 +243,13 @@ void World::render(sf::RenderWindow& window) const
     }
 }
 
+void World::step(const float& stepTime) {
+    player.move(player.currentMoveSpeedX*stepTime,
+                player.currentMoveSpeedY*stepTime);
+	/* Undo last move if the player would end up in a wall. */
+	if (getBlock((int)player.x, (int)player.y) != BlockType::AIR) {
+		player.move(-player.currentMoveSpeedX*stepTime,
+					-player.currentMoveSpeedY*stepTime);
+	}
+    player.rotate(player.currentRotationSpeed*stepTime);
 }