Expressions / adaptation and cleanup after stretch operator removal

The examples have been fixed as well.

examples/filter-points-webgl.js

@@ -21,7 +21,13 @@ const animRatio =
       ['mod',
         ['+',
           ['time'],
-          ['stretch', ['get', 'year'], 1850, 2020, 0, period]
+          [
+            'interpolate',
+            ['linear'],
+            ['get', 'year'],
+            1850, 0,
+            2015, period
+          ]
         ],
         period
       ],
@@ -39,12 +45,14 @@ const style = {
   symbol: {
     symbolType: 'circle',
     size: ['*',
-      ['stretch', ['get', 'mass'], 0, 200000, 8, 26],
-      ['-', 1.5, ['*', animRatio, 0.5]]
+      ['interpolate', ['linear'], ['get', 'mass'], 0, 8, 200000, 26],
+      ['-', 1.75, ['*', animRatio, 0.75]]
     ],
     color: ['interpolate',
+      ['linear'],
       animRatio,
-      newColor, oldColor
+      0, newColor,
+      1, oldColor
     ],
     opacity: ['-', 1.0, ['*', animRatio, 0.75]]
   }

examples/icon-sprite-webgl.js

@@ -26,9 +26,10 @@ const style = {
     size: size,
     color: [
       'interpolate',
-      ['stretch', ['get', 'year'], 1950, 2013, 0, 1],
-      oldColor,
-      newColor
+      ['linear'],
+      ['get', 'year'],
+      1950, oldColor,
+      2013, newColor
     ],
     rotateWithView: false,
     offset: [

examples/webgl-points-layer.js

@@ -28,9 +28,10 @@ const predefinedStyles = {
       size: 18,
       color: [
         'interpolate',
-        ['stretch', ['get', 'population'], 20000, 300000, 0, 1],
-        '#5aca5b',
-        '#ff6a19'
+        ['linear'],
+        ['get', 'population'],
+        20000, '#5aca5b',
+        300000, '#ff6a19'
       ],
       rotateWithView: true
     }
@@ -38,11 +39,23 @@ const predefinedStyles = {
   'circles': {
     symbol: {
       symbolType: 'circle',
-      size: ['stretch', ['get', 'population'], 40000, 2000000, 8, 28],
+      size: [
+        'interpolate',
+        ['linear'],
+        ['get', 'population'],
+        40000, 8,
+        2000000, 28
+      ],
       color: '#006688',
       rotateWithView: false,
       offset: [0, 0],
-      opacity: ['stretch', ['get', 'population'], 40000, 2000000, 0.6, 0.92]
+      opacity: [
+        'interpolate',
+        ['linear'],
+        ['get', 'population'],
+        40000, 0.6,
+        2000000, 0.92
+      ]
     }
   }
 };