I noticed these were out of sync, especially weirdly one mentioning boto and the other mentioning boto3. I figure the list in the README is redundant when the Installation docs section lists the supported libraries, so I've removed it. I also:
* alphabetically sorted the list
* Highlighted the library names as code
* Added both `boto` and `boto3` to the list since there is support for both
* Removed the comment about Tornado's AsyncHTTPClient since that's an implementation detail plus the patch happens on a couple different classes
* Removed the note about `http.client` being part of Python 3, because everyone is Python 3 these days anyway :)
