Added 'O' Shortcut

Added 'O' (Upper case 'o') shortcut to open the file and close
the quickfix window.

README.md

@@ -96,6 +96,7 @@ Some characters have special meaning, and need to be escaped your search pattern
 In the quickfix window, you can use:
 
     o    to open (same as enter)
+    O    to open and close quickfix window
     go   to preview file (open but maintain focus on ack.vim results)
     t    to open in new tab
     T    to open in new tab silently

doc/ack.txt

@@ -77,6 +77,8 @@ The following keyboard shortcuts are available in the quickfix window:
 
 o                   open file (same as enter).
 
+O                   open file and close quickfix window.
+
 go                  preview file (open but maintain focus on ack.vim results).
 
 t                   open in a new tab.

plugin/ack.vim

@@ -73,7 +73,8 @@ function! s:Ack(cmd, args)
     exec "nnoremap <silent> <buffer> t <C-W><CR><C-W>T"
     exec "nnoremap <silent> <buffer> T <C-W><CR><C-W>TgT<C-W><C-W>"
     exec "nnoremap <silent> <buffer> o <CR>"
-    exec "nnoremap <silent> <buffer> go <CR><C-W><C-P>"
+    exec "nnoremap <silent> <buffer> O <CR><C-W><C-W>:ccl<CR>"
+    exec "nnoremap <silent> <buffer> go <CR><C-W><C-W>"
     exec "nnoremap <silent> <buffer> h <C-W><CR><C-W>K"
     exec "nnoremap <silent> <buffer> H <C-W><CR><C-W>K<C-W>b"
     exec "nnoremap <silent> <buffer> v <C-W><CR><C-W>H<C-W>b<C-W>J<C-W>t"