Mark as 0.18-DEV and remove deprecations

[oxinabox]

closes #577

closes #496

Follows up on #603 (comment)
and deprecates find_root

Required to be merged before #547

[davidanthoff]

PLEASE, make it 1.0.0! So that going forward you have the option to do minor, patch and major releases.

[oxinabox]

@davidanthoff see #479

Can't do it this release as it still has deprecations added.
Further there are pending breaking issues still open,
and we haven't completed the audit of the code base to be sure we don't have any Julia 0.3 style constructors, or other issues from not following the Julia 1.0 APIs. (like push! returning the value rather than the collection etc).
I am keen to get to 1.0 also, but not if I know that i will be tagging 2.0 soon after.

[davidanthoff]

I think there is zero harm in a 2.0 shortly after a 1.0, who cares? But going 1.0 now allows you to do minor and patch releases in the meantime, which is a great benefit to downstream packages because it becomes clear what is what. I think this fixation on 1.0 as a somewhat special version really is not a good match with the fact that semver plays an important role in the package resolution story in Julia.

[oxinabox]

While I do agree, in general and personally, I just am not willing to commit to that position on DataStructures.jl.
Because it is such a public package, and that is not the standard the community follows. Not yet at least.
Make the case on any other package I maintained and I would be seriously considering it, but not DataStructures.

(When we started talking about general registry, I argued that it should not accept packages before they tagged 1.0)