This allows applications to create an IOLoop to be started in another
thread without making it current in the originating thread.
Update docs to use IOLoop.current() in place of IOLoop.instance() when
starting the loop.
Closes#1390.
Parameters to the extension are not fully supported (the client side
supports client_no_context_takeover which is mandatory to implement,
but the server rejects any parameters offered by the client, and neither
side supports setting wbits).
Closes#308.
Closes#668.
Browsers that only support draft76 are now less common than those
that do not support websockets at all, so applications should
use their non-websocket workarounds for these browsers.
Pierce Lopez