Documentation and New Layers

I fixed some of the documenation comments of the existing Blob and Queue layers, and, additionally, I added two other layers, PriorityQueue and BlobAsync, to the repository and updated the README to reflect these changes. Finally, there is an additional file, PerformanceTest.java, that tests the speed-up provided by BlobAsync over regular Blobs. It is not technically a layer, and maybe shouldn't be here, but I do need it for an upcoming blob post, for what it's worth.