Ipykernel

failures in nbconvert.

- Fix socket-binding race conditions ([412](https://github.com/ipython/ipykernel/pull/412),
[419](https://github.com/ipython/ipykernel/pull/419))
- Add a no-op `flush` method to `DummySocket` and comply with stream
API ([405](https://github.com/ipython/ipykernel/pull/405))
- Update kernel version to indicate kernel v5.3 support ([394](https://github.com/ipython/ipykernel/pull/394))
- Add testing for upcoming Python 3.8 and PEP 570 positional
parameters ([396](https://github.com/ipython/ipykernel/pull/396), [#408](https://github.com/ipython/ipykernel/pull/408))

5.1.1 fixes a bug that caused cells to get stuck in a busy state.

- Flush after sending replies [390](https://github.com/ipython/ipykernel/pull/390)

- Fix message-ordering bug that could result in out-of-order
executions, especially on Windows [356](https://github.com/ipython/ipykernel/pull/356)
- Fix classifiers to indicate dropped Python 2 support
[354](https://github.com/ipython/ipykernel/pull/354)
- Remove some dead code [355](https://github.com/ipython/ipykernel/pull/355)
- Support rich-media responses in `inspect_requests` (tooltips)
[361](https://github.com/ipython/ipykernel/pull/361)

- Drop support for Python 2. `ipykernel` 5.0 requires Python >= 3.4
- Add support for IPython's asynchronous code execution
[323](https://github.com/ipython/ipykernel/pull/323)
- Update release process in `CONTRIBUTING.md` [339](https://github.com/ipython/ipykernel/pull/339)