* jupyter/messages.scm (%current-protocol-version): New variable.
(<language-info>, <kernel-info-reply>): New record types.
* guix/jupyter/kernel.scm: New file.
* Makefile.am (SOURCES): Add it.
* guix-jupyter-kernel.scm (KERNEL-INFO): Remove.
(reply-kernel-info-request): Use 'kernel-info-reply->json'.
* tests/kernels.scm ("kernel_info_request"): Use
'json->kernel-info-reply' and associated record types.