Use slightly flatter directory structure since some developers did not

like too many folders.
Extracted code from some files into separate files to fit with the new
layout.

src/maths.c

@@ -0,0 +1,42 @@
+#include <math.h>
+
+#include "maths.h"
+
+int constrain(int amt, int low, int high)
+{
+    if (amt < low)
+        return low;
+    else if (amt > high)
+        return high;
+    else
+        return amt;
+}
+
+void devClear(stdev_t *dev)
+{
+    dev->m_n = 0;
+}
+
+void devPush(stdev_t *dev, float x)
+{
+    dev->m_n++;
+    if (dev->m_n == 1) {
+        dev->m_oldM = dev->m_newM = x;
+        dev->m_oldS = 0.0f;
+    } else {
+        dev->m_newM = dev->m_oldM + (x - dev->m_oldM) / dev->m_n;
+        dev->m_newS = dev->m_oldS + (x - dev->m_oldM) * (x - dev->m_newM);
+        dev->m_oldM = dev->m_newM;
+        dev->m_oldS = dev->m_newS;
+    }
+}
+
+float devVariance(stdev_t *dev)
+{
+    return ((dev->m_n > 1) ? dev->m_newS / (dev->m_n - 1) : 0.0f);
+}
+
+float devStandardDeviation(stdev_t *dev)
+{
+    return sqrtf(devVariance(dev));
+}