Updates for new configuration system - #57

This is the correct approach, but it requires astropy 0.4 as a minimum. I had intended to not make this change until 0.4 + 1 was out, since the old 0.3 approach will still work.

@mdboom - ok, that makes sense!

Yes, I am working on an affiliated package that has no desire to be compatible with astropy 0.3. Sorry for the confusion.

Has this been implemented by #51 or should this still be merged?

@cdeil - #51 was closed without merging and this PR is a spinoff from there. As indicated by @mdboom, we should do this close to the 1.0 release since the old way still works in the 0.4 series of Astropy.

@astrofrog - Can you rebase this?

@mdboom - now that 1.0 is out, shall we go ahead and make the changes? I think supporting 0.4+ now is fine for affiliated packages?

So I think the actual change to _astropy_init.py was made by @mdboom in 74f4799 - I will now rebase to just add the example, in case people want to include it.

@cdeil @pllim - rebased

Not sure why I'm listed as one of the commit authors. But the PR looks good. Thanks!

@pllim - you made this original PR ages ago, and this is a rebased version of that :)

This also will need some updates to the docs about setting up an affiliated package to remind people to remove the config file if not needed.

@astrofrog -- 👍 to this

We're moving over to cookicutter, so I'm closing old unresolved PRs. Please reopen against the cookicutter branch if you feel this is still relevant.