skawarePackages.buildManPages: derivation wrapper for skaware man page ports

GitHub user flexibeast has been porting the html documentation from
skarnet.org to mdoc, making them available as man pages. While the
documentation is non authorative, it is certainly useful and is also
linked from skarnet.org.

buildManPages implements the common mkDerivation machinery common to all
ported man page packages / repositories.

pkgs/build-support/skaware/build-skaware-man-pages.nix

···
+{ lib, stdenv, fetchFromGitHub }:
+
+{
+  # : string
+  pname
+  # : string
+, version
+  # : string
+, sha256
+  # : list (int | string)
+, sections
+  # : string
+, description
+  # : list Maintainer
+, maintainers
+  # : license
+, license ? lib.licenses.isc
+  # : string
+, owner ? "flexibeast"
+  # : string
+, rev ? "v${version}"
+}:
+
+let
+  manDir = "${placeholder "out"}/share/man";
+
+  src = fetchFromGitHub {
+    inherit owner rev sha256;
+    repo = pname;
+  };
+in
+
+stdenv.mkDerivation {
+  inherit pname version src;
+
+  makeFlags = [
+    "MANPATH=${manDir}"
+  ];
+
+  dontBuild = true;
+
+  preInstall = lib.concatMapStringsSep "\n"
+    (section: "mkdir -p \"${manDir}/man${builtins.toString section}\"")
+    sections;
+
+  meta = with lib; {
+    inherit description license maintainers;
+    inherit (src.meta) homepage;
+    platforms = platforms.all;
+  };
+}

pkgs/top-level/all-packages.nix

···
     buildPackage = callPackage ../build-support/skaware/build-skaware-package.nix {
       inherit cleanPackaging;
     };
+    buildManPages = callPackage ../build-support/skaware/build-skaware-man-pages.nix { };
 
     skalibs = callPackage ../development/libraries/skalibs { };
     execline = callPackage ../tools/misc/execline { };