Refactor attribute calculations to be DRYer

- Create `scaleInRange()` function to eliminate repeated calculations using the same formula.
- Rename `linear_scale_factor` to the more descriptive `width_ratio` (where value at `minWidth` would be 0 and at `maxWidth` would be 1), which might also be more sensible to use in easing-curve calculations in the future.

src/textblock.js

@@ -44,17 +44,19 @@ window.Textblock = function(textblocks) {
         tb_maxw
       ); // cap current container width to minWidth and maxWidth settings
 
-      var linear_scale_factor =
-        (current_width_capped - tb_minw) / (tb_maxw - tb_minw);
+      var width_ratio = (current_width_capped - tb_minw) / (tb_maxw - tb_minw);
 
       return {
-        fontSize: tb_minf + (tb_maxf - tb_minf) * linear_scale_factor,
-        lineHeight: tb_minl + (tb_maxl - tb_minl) * linear_scale_factor,
+        fontSize: scaleInRange(tb_minf, tb_maxf, width_ratio),
+        lineHeight: scaleInRange(tb_minl, tb_maxl, width_ratio),
         fontVariationSettings:
-          '"wght" ' + (tb_ming + (tb_maxg - tb_ming) * linear_scale_factor)
+          '"wght" ' + scaleInRange(tb_ming, tb_maxg, width_ratio)
       };
     }
   }
+  function scaleInRange(min, max, scale_factor) {
+    return min + (max - min) * scale_factor;
+  }
   function prepBlockSettings(block) {
     var defaultSettings = {
       minWidth: 320,