Ipykernel

- Publish all IO in a thread, via `IOPubThread`. This solves the problem of requiring
`sys.stdout.flush` to be called in
the notebook to produce output promptly during long-running cells.

- Remove references to outdated IPython guiref in kernel banner.

- Patch faulthandler to use `sys.__stderr__` instead of forwarded
`sys.stderr`, which has no fileno when forwarded.

- Deprecate some vestiges of the Big Split:

- `ipykernel.find_connection_file`
is deprecated. Use
`jupyter_client.find_connection_file` instead.

\- Various pieces of code specific to IPython parallel are
deprecated in ipykernel and moved to ipyparallel.

- Don't show interactive debugging info when kernel crashes
- Fix handling of numerical types in json_clean
- Testing fixes for output capturing

- Fix default display name back to "Python X" instead of "pythonX"

- Support sending a full message in initial opening of comms
(metadata, buffers were not previously allowed)
- When using `ipython kernel install --name` to install the IPython
kernelspec, default display-name to the same value as `--name`.