Create map-number-range.md

map-number-range.md

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+### mapNumRange
+
+Maps a number range to another number range.
+
+Returns a number mapped from the in range to the out range. 
+
+```js
+const mapNumRange = (num, in_min, in_max, out_min, out_max) => {
+    return (num - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+  }
+```
+
+```js
+mapNumRange(5,0,10,0,100); // '50'
+```