* jupyter-rest-api.el: Ensure strings are encoded before making HTTP request.
(jupyter-api-http-request): Encode JSON as utf-8.
(jupyter-api-xsrf-header-from-cookies): Ensure header isn't multibyte.
(jupyter-api-authenticate): For the token method, ensure token isn't multibyte.
(jupyter-api-copy-file): Encode string before encoding to base64 for binary content.
(jupyter-api-read-file-content): Decode content as utf-8 when necessary.
* jupyter-tramp.el
(jupyter-tramp-write-region): Ensure only `utf-8` or `binary` coding systems
are used since Jupyter only supports those.
* test/jupyter-tramp-test.el: Update for above changes.
* jupyter-rest-api.el (jupyter-api-content-buffer): New function.
(jupyter-api-insert-model-content): Use it.
* jupyter-tramp.el (jupyter-tramp-file-local-copy): Use it.
* Start notebook on-demand during tests
* Do cleanup of sockets/processes when killing Emacs
* This should work around intermittent core dumps on Travis due to epoll
reconnect attempts.
* Simplify tests by creating and using setup/teardown macros
