(fix) large step count move on Nano Every #96

Use `labs()` explicitly when `abs()` was needed for `long` parameters.

Reason:
On Arduino Nano Every (ATmega4809), `int abs(int)` is used for a `long` argument,
resulting in failure to move more than 32767 steps in one move operation.

examples/UnitTest/UnitTest.ino

@@ -63,7 +63,7 @@ bool result(float rpm, int microstep, int steps, long elapsed_micros, long expec
     char t[128];
     float error = float(elapsed_micros) / float(expected_micros);
     unsigned step_micros = expected_micros / steps;
-    unsigned error_micros = abs(elapsed_micros - expected_micros) / steps;
+    unsigned error_micros = labs(elapsed_micros - expected_micros) / steps;
     sprintf(t, "  rpm=%-4d expected=%10luµs elapsed=%10luµs step_err=%6uµs avgstep=%6uµs", 
             int(rpm), expected_micros, elapsed_micros, error_micros, step_micros);
     Serial.print(t);

src/BasicStepperDriver.cpp

@@ -124,7 +124,7 @@ void BasicStepperDriver::startMove(long steps, long time){
     // set up new move
     dir_state = (steps >= 0) ? HIGH : LOW;
     last_action_end = 0;
-    steps_remaining = abs(steps);
+    steps_remaining = labs(steps);
     step_count = 0;
     rest = 0;
     switch (profile.mode){

src/SyncDriver.cpp

@@ -21,7 +21,7 @@ void SyncDriver::startMove(long steps1, long steps2, long steps3){
      */
     long move_time = 0;
     FOREACH_MOTOR(
-        long m = motors[i]->getTimeForMove(abs(steps[i]));
+        long m = motors[i]->getTimeForMove(labs(steps[i]));
         if (m > move_time){
             move_time = m;
         }