Add new plugin to Neovim for easier merges

I'll give it a try and check how well it works.

home/programs/git.nix

@@ -107,11 +107,16 @@
 
     merge = {
       ff = true;
-      tool = "nvimdiff4";
+      tool = "new";
+      conflictStyle = "diff3";
     };
 
     "mergetool \"nvimdiff4\"" = {
       cmd = "${pkgs.neovim}/bin/nvim -d $LOCAL $BASE $REMOTE $MERGED -c '$wincmd w' -c 'wincmd J' -c 'diffoff'";
     };
+    "mergetool \"new\"" = {
+      cmd = "${pkgs.neovim}/bin/nvim -f $MERGED $BASE $LOCAL $REMOTE -c 'MergetoolStart'";
+      trustExitCode = true;
+    };
   };
 }

home/programs/neovim.nix

@@ -267,7 +267,14 @@ in {
       '';
     }
 
-    vim-fugitive
+    fugitive
+    {
+      plugin = vim-mergetool;
+      config = ''
+        let g:mergetool_layout = 'b,lr,m'
+      '';
+    }
+
     vim-commentary
     vim-indent-object
     vim-textobj-comment