Get rid of `later_proper'`

See merge request FP/iris-coq!82

add later_ne; make later_proper match the other _proper lemmas

See merge request FP/iris-coq!81

This reverts commit 849abb8d, reversing changes
made to 8de0b894.  The merge was done
accidentally, before review happened.

Add progress bit to WP.

See merge request FP/iris-coq!37

This is derived from `wp_forget_not_stuck` and a trivial preorder on
stuckness bits. (The two lemmas are redundant, but I have examples
where each seems more natural than the other.)

I did *not* bake `wp_stuckness_mono` into `strong_mono` for two
reasons. Mainly, I didn't see a nice way to combine the two proofs
(beyond `cut`). Less important, changing the type of `wp_strong_mono`
will break code.

I saw no need for `stuckness_flip`: strong atomicity always works,
while weak atomicity works only for expressions that are not stuck.
Since this seemed unclear, I split lemma `wp_atomic'` up into
`wp_strong_atomic` (parametric in the WP's `s`) and `wp_weak_atomic`
(not). The proof mode instance is stated in terms of the derived rule
`wp_atomic` (parametric in `s`).

Pull progress bit out of the WP fixpoint,
make (most) wp adequacy notation only parsing, and
generalize forget_progress.

rename sub_values -> sub_redexes_are_values

See merge request FP/iris-coq!79

Make atomic a type class.

See merge request FP/iris-coq!78