Add UltiSnips

UltiSnips is a snippet manager, but it also requires a directory to
store its so-called "snippets". This installs UltiSnips into the vim
configuration and also creates a path within .vim to store those
snippets. Perhaps in the future it will make sense to make a separate
repo (or a flake) out of those.

home/default.nix

@@ -14,6 +14,11 @@
     text = "keep";
   };
 
+  home.file.".vim/snips/.keep" = {
+    enable = true;
+    text = "keep";
+  };
+
   home.packages = with pkgs; [
     ripgrep
     gh

home/programs/vim.nix

@@ -23,6 +23,7 @@
         vim-helm
         pkgs.vim-bicep
         vim-terraform
+        ultisnips
       ];
       extraConfig = ''
         colorscheme space_vim_theme
@@ -32,6 +33,8 @@
 
         set directory=~/.vim/swapfiles
 
+        let g:UltiSnipsSnippetDirectories = ["snips"]
+
         map <Leader>e <Plug>(easymotion-prefix)
 
         nnoremap <leader>gs :Git<CR>