Add kword context to asynchronous call

This is a great combination of two awesome libraries, but I found myself needing to persist context across the calls that were made. My initial hack around this was to do work based on the URL, but that value is subject to change based on the website you are querying. 

I added in the context shortcut even though I could use the existing "get" just to ensure everything would continue to work properly regardless of an update. Also, I added into the documentation, but that was really only for my purposes, so I would know I had modified this library. 

If you choose not to add this in, no worries. Just thought it could help others!