In %magic help, remove duplicate aliases

[fperez]

Certain magics are actually just aliases of another, like %hist and %history. In %magic, we show the full help for both, which can be confusing. We should instead indicate which one is an alias and refer the reader to the original for details.

[bfroehle]

I agree this would be a nice improvement. In terms of implementation, I think it'd be easiest to add an attribute to the function which stored the name of the alias:

    # For a long time we've had %hist as well as %history
    @line_magic
    def hist(self, arg):
        return self.history(arg)

    hist.__doc__ = history.__doc__
    hist._magic_alias = 'history'

Then %magic can just check for fn._magic_alias and print an abbreviated description:

%history:
    Alias for `%hist`.

We could optionally provide a function which did this wrapping automatically:

    hist = line_magic_alias('hist', history)

[fperez]

@bfroehle, +1