ipfs-shell [1] accesses the Command objects directly to construct
requests for an external IPFS daemon API.  This isn't a terribly
robust approach, because it doesn't handle version differences between
the version of go-ipfs used to build the daemon and the version used
to build the ipfs-shell-consuming application.  But for cases where
you can get those APIs to match it works well.  Making these two
commands public allows us to write ipfs-shell wrappers for them.
Until we figure out how to get ipfs-shell working without access to
core/commands, I think the best approach is to make future command
objects and their returned structures public, and to go back and
expose existing commands/structures on an as-needed basis.

In this case, I need the public PublishCmd for the Docker-registry
storage driver, and I made the IpnsCmd public at the same time to stay
consistent for both 'ipfs name ...' sub-commands.

[1]: https://github.com/whyrusleeping/ipfs-shell

License: MIT
Signed-off-by: W. Trevor King <wking@tremily.us>