Do not support coq < v8.16 anymore

Coq v8.19 dropped the old & deprecated stdlib sections concerning `Even`
and `Odd`. The new definitions that need to be used are only available
since Coq v8.16. So support for these needs to be dropped or the
relevant sections would need to be backported to Coq v8.12 to v8.15.

Coq v8.16 was released in September 2022 and according to
https://repology.org/project/coq/versions most major distributions have
at least v8.16 available.

Problem: Hydra-battles uses zorns-lemma as a dependency and currently
supports from v8.14 onwards. A new release of zorns-lemma would force
hydra-battles to upgrade as well.

The problematic parts of the stdlib are only used in `coq-topology` but not
in `coq-zorns-lemma`. So it would be possible to only drop support for
versions < v8.16 in `coq-topology` and keep the other versions in
`coq-zorns-lemma`. But this would require changes in the
GitHub-Workflows which I don't yet know how to do.

.github/workflows/coq-ci.yml

@@ -20,10 +20,6 @@ jobs:
           - 'coqorg/coq:8.18'
           - 'coqorg/coq:8.17'
           - 'coqorg/coq:8.16'
-          - 'coqorg/coq:8.15'
-          - 'coqorg/coq:8.14'
-          - 'coqorg/coq:8.13'
-          - 'coqorg/coq:8.12'
       fail-fast: false
     steps:
       - uses: actions/checkout@v2

README.md

@@ -36,7 +36,7 @@ and results of general topology in Coq.
   - stop-cran ([**@stop-cran**](https://github.com/stop-cran))
   - Columbus240 ([**@Columbus240**](https://github.com/Columbus240))
 - License: [GNU Lesser General Public License v2.1 or later](LICENSE)
-- Compatible Coq versions: Coq 8.12 or later (use the corresponding branch or release for other Coq versions)
+- Compatible Coq versions: Coq 8.16 or later (use the corresponding branch or release for other Coq versions)
 - Additional dependencies:
   - Zorn's Lemma (set library that is part of this repository)
 - Coq namespace: `Topology`

coq-topology.opam

@@ -16,7 +16,7 @@ and results of general topology in Coq.
 build: ["dune" "build" "-p" name "-j" jobs]
 depends: [
   "dune" {>= "2.5"}
-  "coq" {(>= "8.12" & < "8.20~") | (= "dev")}
+  "coq" {(>= "8.16" & < "8.20~") | (= "dev")}
   "coq-zorns-lemma" {= version}
 ]
 

coq-zorns-lemma.opam

@@ -17,7 +17,7 @@ was as support for the Topology library.
 build: ["dune" "build" "-p" name "-j" jobs]
 depends: [
   "dune" {>= "2.5"}
-  "coq" {(>= "8.12" & < "8.20~") | (= "dev")}
+  "coq" {(>= "8.16" & < "8.20~") | (= "dev")}
 ]
 
 tags: [