This also solves a name clash with the extension order of CMRAs.

This reverts commit 20b4ae55, which does
not seem to work with Coq 8.5pl2 (I accidentally tested with 8.5pl1).

This makes type checking more directed, and somewhat more predictable.

On the downside, it makes it impossible to declare the singleton on
lists as an instance of SingletonM and the insert and alter operations
on functions as instances of Alter and Insert. However, these were not
used often anyway.

There was not really a need for the lattice type classes, so I removed
these.

Thanks to Amin Timany for the suggestion.

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.

The singleton maps notation is now also more consistent with the
insert <[_ := _]> _ notation for maps.

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

Also do some minor clean up.