This replaces f_equiv and solve_proper with our own, hopefully better, versions

simplify_equality        => simplify_eq
simplify_equality'       => simplify_eq/=
simplify_map_equality    => simplify_map_eq
simplify_map_equality'   => simplify_map_eq/=
simplify_option_equality => simplify_option_eq
simplify_list_equality   => simplify_list_eq
f_equal'                 => f_equal/=

The /= suffixes (meaning: do simpl) are inspired by ssreflect.

Also, make our redefinition of done more robust under different
orders of Importing modules.

Since Coq 8.4 did not backtrack on eauto premises, we used to ensure
that hints like

  Hint Extern 0 (?x ≡{_}≡ ?y) => reflexivity.

were not used for goals involving evars by writing ?x ≡{_}≡ ?y instead
of _ ≡{_}≡ _.

This seems to be a legacy issue that no longer applies to Coq 8.5, so
I have removed these restrictions making these hints thus more powerful.

Also do some minor clean up.

This way we avoid many one-off indexes and no longer need special cases for
index 0 in many definitions. For example, the definition of the distance
relation on option and excl has become much easier. Also, uPreds no longer need
to hold at index 0.

In order to make this change possible, we had to change the notions of
"contractive functions" and "chains" slightly.

Thanks to Aleš Bizjak and Amin Timany for suggesting this change and to help
with the proofs.

* Insert and singleton operation.
* Identity element.
* Non-expansiveness and properness of insert and singleton.
* Frame preserving updates.
* Functoriality.

Instead, we have just a construction to create a CMRA from a RA. This
construction is also slightly generalized, it now works for RAs over any
timeless COFE instead of just the discrete COFE.

Also:
* Put tactics and big_ops for CMRAs in a separate file.
* Valid is now a derived notion (as the limit of validN), so it does not have
  to be defined by hand for each CMRA.

Todo:
Make the constructions DRA -> CMRA and RA -> CMRA more uniform.

* Framepreserving updates are now on CMRAs rather than RAs
* Excl and auth are now CMRAs
* Show that excl and auth are functors
* STS is now an CMRA