Add Ack plugin with Ag support

.gitmodules

@@ -62,3 +62,6 @@
 [submodule "pack/plugins/start/nerdtree"]
 	path = pack/plugins/start/nerdtree
 	url = https://github.com/preservim/nerdtree.git
+[submodule "pack/plugins/start/ack"]
+	path = pack/plugins/start/ack
+	url = git@github.com:mileszs/ack.vim.git

pack/plugins/start/ack

@@ -0,0 +1 @@
+Subproject commit 36e40f9ec91bdbf6f1adf408522a73a6925c3042

vimrc

@@ -18,6 +18,10 @@ set signcolumn=yes
 set rtp+=~/.fzf
 map ; :Files<CR>
 
+if executable('ag')
+  let g:ackprg = 'ag --vimgrep'
+endif
+
 colorscheme onehalfdark
 if exists('+termguicolors') && ($COLORTERM == "24bit" || $COLORTERM == "truecolor")
   let &t_8f = "\<Esc>[38;2;%lu;%lu;%lum"
@@ -82,6 +86,7 @@ nnoremap <leader>n :NERDTreeFocus<CR>
 nnoremap <C-n> :NERDTree<CR>
 nnoremap <C-t> :NERDTreeToggle<CR>
 nnoremap <C-f> :NERDTreeFind<CR>
+nnoremap <Leader>a :Ack!<Space>
 
 " Exit Vim if NERDTree is the only window remaining in the only tab.
 autocmd BufEnter * if tabpagenr('$') == 1 && winnr('$') == 1 && exists('b:NERDTree') && b:NERDTree.isTabTree() | quit | endif