Add option.installWithSymlinks to toggle symlink usage

If enabled, the default assest.install will use symlinks rather then copying.

lib/assets/Assets.js

@@ -4,7 +4,7 @@ var fs = require("fs-extra");
 var path = require("path");
 var URI = require("../util/URI");
 var debug = require("../util/debug");
-
+var ensureSymlink = require("ensure-symlink");
 var AssetsCollection = require("./AssetsCollection");
 // TODO - remove when deprecated AssetPathEntry is removed
 var AssetsSource = require("./AssetsSource");
@@ -172,8 +172,13 @@ Assets.prototype.install = function(file, uri, cb) {
     var dest = path.join(options.buildDir, uri);
 
     try {
-      // we explicitly use copySync rather than copy to avoid starving system resources
-      fs.copySync(file, dest);
+      if (options.installWithSymlinks) {
+        fs.mkdirpSync(path.dirname(dest));
+        ensureSymlink(file, dest);
+      } else {
+        // we explicitly use copySync rather than copy to avoid starving system resources
+        fs.copySync(file, dest);
+      }
       cb(null, dest);
     } catch (error) {
       error = new Error("Failed to install asset from " + file + "\n" + error.toString());

package.json

@@ -31,6 +31,7 @@
     "archy": "^1.0.0",
     "deasync": "^0.1.4",
     "debug": "^2.2.0",
+    "ensure-symlink": "^1.0.0",
     "fs-extra": "^0.30.0",
     "glob": "^7.1.0",
     "lodash.includes": "^4.3.0",