Switch to libvips' resize, make fastShrinkOnLoad optional (#977)

lib/constructor.js

@@ -149,6 +149,7 @@ const Sharp = function (input, options) {
     kernel: 'lanczos3',
     interpolator: 'bicubic',
     centreSampling: false,
+    fastShrinkOnLoad: true,
     // operations
     background: [0, 0, 0, 255],
     flatten: false,

lib/resize.js

@@ -142,6 +142,11 @@ function resize (width, height, options) {
     if (is.defined(options.centreSampling)) {
       this._setBooleanOption('centreSampling', options.centreSampling);
     }
+
+    // Shrink on load
+    if (is.defined(options.fastShrinkOnLoad)) {
+      this._setBooleanOption('fastShrinkOnLoad', options.fastShrinkOnLoad);
+    }
   }
   return this;
 }