So as to further generalize and separate out the abstract kernel manager class
from its various implementations.
* jupyter-kernel-manager.el (jupyter-meta-kernel): Fix documentation.
(jupyter-kernel-process, jupyter-command-kernel, jupyter-spec-kernel):
Move related functions and methods to `jupyter-kernel-process-manager.el`
(jupyter-kernel-manager-base): Remove class.
(jupyter-kernel-manager): Re-purpose class as the base class of all kernel
managers. The class corresponding to the old functionality is now named
`jupyter-kernel-process-manager`. Move all related functions and methods for
`jupyter-kernel-process-manager` to `jupyter-kernel-process-manager.el`.
* jupyter-kernel-process-manager.el: New file.
* jupyter-repl.el: Require `jupyter-kernel-process-manager` instead of
`jupyter-kernel-manager`.
* jupyter-server.el (jupyter-server-kernel-manager): Inherit from
`jupyter-kernel-manager` instead of `jupyter-kernel-manager-base`.
* test/jupyter-test.el (jupyter-kernel-lifetime)
(jupyter-command-kernel): Use `jupyter-kernel-process-manager` instead of
`jupyter-kernel-manager`.
* test/test-helper.el: Require `jupyter-kernel-process-manager` instead of
`jupyter-kernel-manager`.
See #161
* jupyter-rest-api.el (jupyter-api--delete-cookie):
(jupyter-api-delete-cookies): New functions.
* jupyter-server.el (jupyter-gc-servers): Do it.
* test/jupyter-server-test.el (jupyter-api-delete-cookies): New test.
