Account for implementation of modulo

In C++, the % operator, which is normally the modulo operator, is
actually implemented as a division remainder function, which is subtly
different.
In mathematics, both functions would return the same thing, i.e. the
remainder of the division of two numbers. However, while the remainder
in modular arithmetic is always (taken as) positive, the remainder in
division can be negative if either the dividend or divisor is negative.

Since there is currently no scenario in which physicalAngle should
naturally become negative, the solution chosen has been to add 270
degrees to physicalAngle, instead of subtracting 90 degrees (due to the
rotation of the simulator).

source/mega/simulator/simulator.ino

@@ -166,7 +166,7 @@ void respond(scanResponse scanResp) {
 }
 
 void respond(compassCommand* com) {
-  SPI_Wrapper::sendCompassResponse(com->uniqueID, ((physicalAngle - 90) % 360), true);
+  SPI_Wrapper::sendCompassResponse(com->uniqueID, ((physicalAngle + 270) % 360), true);
 }
 
 void moveRobot(moveCommand* com) {