Factored Stepgen2, StepGen3 is a copy of Stepgen2

Firmware/include/extend32to64.h

@@ -0,0 +1,14 @@
+#ifndef EXTEND32TO64
+#define EXTEND32TO54
+
+#include <Arduino.h>
+
+class extend32to64
+{
+public:
+    int64_t previousTimeValue = 0;
+    const uint64_t ONE_PERIOD = 4294967296;  // almost UINT32_MAX;
+    const uint64_t HALF_PERIOD = 2147483648; // Half of that
+    int64_t extendTime(uint32_t in);
+};
+#endif