Samples for batch PDF and image annotation. (#347)

* Added the two samples for pdf annotation

* Added the sample for image batch annotation

* Fixed coding style after running eslint

* Several changes made based on Justin's comments.

* Separated the samples and tests per Justin's comments.

* Using const instead of let

* Changed the description of the tests.

* Replaced tabs with spaces

* Update samples/vision_async_batch_annotate_images_beta.js

Co-Authored-By: happyhuman <happyhuman@users.noreply.github.com>

* Update samples/vision_batch_annotate_files_beta.js

Co-Authored-By: happyhuman <happyhuman@users.noreply.github.com>

* Update samples/vision_batch_annotate_files_beta.js

Co-Authored-By: happyhuman <happyhuman@users.noreply.github.com>

* Update samples/vision_async_batch_annotate_images_beta.js

Co-Authored-By: happyhuman <happyhuman@users.noreply.github.com>

* Update samples/vision_async_batch_annotate_images_beta.js

Co-Authored-By: happyhuman <happyhuman@users.noreply.github.com>

* Renamed the files per Justin's suggestions.

* Edited README file

* Fixed the issue with renaming.

* Dashes instead of underscores

* Corrected the file names in test files.

packages/google-cloud-vision/samples/README.md

@@ -94,6 +94,9 @@ Examples:
   node detect.js pdf my-bucket my-pdf.pdf
   node detect.js localize-objects ./resources/duck_and_truck.jpg
   node detect.js localize-objects-gcs gs://bucket/bucketImage.png
+  node batch_annotate_files.js my-pdf.pdf
+  node batch_annotate_files_gcs.js my-pdf.pdf
+  node async_batch_annotate_images.js gs://bucket/bucketImage.png gs://bucket/out
 
 For more information, see https://cloud.google.com/vision/docs
 ```