termonad: add meta.mainProgram to easily run with flakes

This also adds a top-level `termonad` alias for
`termonad-with-packages`.

pkgs/applications/terminal-emulators/termonad/default.nix

···
-{ stdenv, ghcWithPackages, makeWrapper, packages ? (pkgSet: []) }:
+{ stdenv, haskellPackages, makeWrapper, packages ? (pkgSet: []) }:
 
 let
-  termonadEnv = ghcWithPackages (self: [ self.termonad ] ++ packages self);
+  termonadEnv = haskellPackages.ghcWithPackages (self: [ self.termonad ] ++ packages self);
 in stdenv.mkDerivation {
   name = "termonad-with-packages-${termonadEnv.version}";
 
···
   # trivial derivation
   preferLocalBuild = true;
   allowSubstitutes = false;
+
+  meta = haskellPackages.termonad.meta // {
+    mainProgram = "termonad";
+  };
 }

pkgs/top-level/all-packages.nix

···
   };
   termite-unwrapped = callPackage ../applications/terminal-emulators/termite { };
 
-  termonad-with-packages = callPackage ../applications/terminal-emulators/termonad {
-    inherit (haskellPackages) ghcWithPackages;
-  };
+  termonad-with-packages = callPackage ../applications/terminal-emulators/termonad { };
+
+  termonad = termonad-with-packages;
 
   termsyn = callPackage ../data/fonts/termsyn { };