initialize_subcommand does not print help

[ipython]

initialize_subcommand does not print help

[minrk]

The string associated with a subcommand is what shows up in the parent's help output:

ipython -h
...
Subcommands
-----------

Subcommands are launched as `ipython cmd [args]`. For information on using
subcommand 'cmd', do: `ipython cmd -h`.

kernel
    Start a kernel without an attached frontend.
nbconvert
    DEPRECATED: Convert notebooks to/from other formats.
kernelspec
    DEPRECATED: Manage Jupyter kernel specifications.
install-nbextension
    DEPRECATED: Install Jupyter notebook extension files
profile
    Create and manage IPython profiles.
console
    DEPRECATED: Launch the Jupyter terminal-based Console.
notebook
    DEPRECATED: Launch the Jupyter HTML Notebook Server.
qtconsole
    DEPRECATED: Launch the Jupyter Qt Console.
locate
    print the path to the IPython dir
trust
    DEPRECATED: Sign notebooks to trust their potentially unsafe contents at load.
history
    Manage the IPython history database.

If we want to show a message when dispatching to the deprecated subcommands, it's going to mean extra code to run prior to dispatching. Perhaps deprecated subcommands should be a separate collection?

[Carreau]

If we want to show a message when dispatching to the deprecated subcommands, it's going to mean extra code to run prior to dispatching. Perhaps deprecated subcommands should be a separate collection?

Probably otherwise people dont' get a message when they actually use the subcommand (like on SO):

$ ipython kernelspec
No subcommand specified. Must specify one of: ['install', 'install-self', 'list']

Manage Jupyter kernel specifications.

Subcommands
-----------

Subcommands are launched as `jupyter kernelspec cmd [args]`. For information on
using subcommand 'cmd', do: `jupyter kernelspec cmd -h`.

install
    Install a kernel specification directory.
install-self
    [DEPRECATED] Install the IPython kernel spec directory for this Python.
list
    List installed kernel specifications.

I see that the install-self is deprecated, but it would be nice to see that kernelspec itself is deprecated.

[Carreau]

Actually we can just make a dummy wrapper around 'jupyter_client.kernelspecapp.KernelSpecApp' that log a stderr message when used, and change the alias to point to the deprecated wrapper.