add javascript binding and file picker for web

webgl/src/mylib.js

@@ -0,0 +1,28 @@
+function js_pick_file(fn) {
+    var input = document.createElement('input');
+    input.type = 'file';
+    
+    input.onchange = function(e) { 
+      // getting a hold of the file reference
+      var file = e.target.files[0]; 
+  
+      // setting up the reader
+      var reader = new FileReader();
+      reader.readAsArrayBuffer(file);
+      //reader.readAsText(file,'UTF-8');
+      // here we tell the reader what to do when it's done reading...
+      reader.onload = function(readerEvent) {
+        console.log("reader.onload " + file.name);
+        var content = new Uint8Array(readerEvent.target.result); // this is the content!
+        console.log( content );
+        FS.writeFile(file.name, content);
+        Module.TaskCallback_call(fn, file.name);
+        Module.TaskCallback_delete(fn);
+      }
+    }
+    
+    input.click();
+}
+mergeInto(LibraryManager.library, {
+  js_pick_file: js_pick_file,
+});