This generalizes Fix_unfold to a setoid setting. In particular,
we can use this to unfold multi-argument fixpoints without
requiring functional extensionality.

Infinity is described by having an injection from nat.

Provide a pretty-printer for [nat].

See merge request robbertkrebbers/coq-stdpp!15

Minor documentation fixes

See merge request robbertkrebbers/coq-stdpp!14

The documentation for some typeclasses used the wrong
names for these typeclasses.

Notation for disjointness: replace ⊥ with ##, so that ⊥ can be used for bottom.

See merge request robbertkrebbers/coq-stdpp!12

This addresses some concerns in !5.

Add monadic `;;` and change level of the do-notation to 100

See merge request robbertkrebbers/coq-stdpp!10

This way, we will be compabile with Iris's heap_lang, which puts ;;
at level 100.

Add more lemmas for gmap uncurry

See merge request robbertkrebbers/coq-stdpp!9

Add more properties of intersection_with for fin_maps

See merge request robbertkrebbers/coq-stdpp!7

Add lemma lookup_gmap_uncurry_empty

See merge request robbertkrebbers/coq-stdpp!8