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.

Player.cpp

@@ -25,4 +25,21 @@ void Player::rotate(float alpha)
     {
         orientation += 360;
     }
+
+	/*
+	 * Rotate the movement vector along the new angle, assumes that the only
+	 * speed influencing the player is its own movement.
+	 */
+	float prevSpeedX = currentMoveSpeedX;
+	float prevSpeedY = currentMoveSpeedY;
+	currentMoveSpeedX = cosf(-alpha * deg_to_rad) * prevSpeedX
+					    - sinf(-alpha * deg_to_rad) * prevSpeedY;
+	currentMoveSpeedY = sinf(-alpha * deg_to_rad) * prevSpeedX
+					    + cosf(-alpha * deg_to_rad) * prevSpeedY;
+}
+
+void Player::updateSpeed(float localX, float localY) {
+	// TODO: Support strafing.
+	currentMoveSpeedX = localX * sinf(orientation*deg_to_rad)*moveSpeed;
+	currentMoveSpeedY = localX * cosf(orientation*deg_to_rad)*moveSpeed;
 }