Automatically load extension if available

[bclyons12]

This is similar to the idea here, but I don’t see this particular point resolved in the thread.

Are extension packages importable?

To be concrete, suppose the package Foo has an extension Ext which depends on Bar and Baz. Then it may be nice to let pkg> add Foo[Ext] be a shorthand for pkg> add Foo, Bar, Baz (thus allowing the fact that Ext depends on Bar and Baz to be an implementation detail). And further, it may be nice to let import Foo[Ext] be a shorthand for import Foo, Bar, Baz const Ext = Base.get_extension(Foo, :Ext)

I wouldn’t need the actual Ext extension module exposed to the REPL, just a shorthand to load the necessary packages.