title: magit-grep, how to include or exlude file extensions?
body: <p>I'd like to give some options to magit-grep </p>
  
  <p>running it with option <code>foo</code> results in </p>
  
  <pre><code>git --no-pager grep -n foo
  </code></pre>
  
  <p>I'd like to give options to it </p>
  
  <pre><code>git --no-pager grep -n foo (options to include *.html and exclude *.py, etc)
  </code></pre>
  
  <p>It doesn't have to be magit-grep,  what's the best git grep solution in emacs?   </p>
  
  <hr>
  
  <p>magit-grep</p>
  
  <pre class="lang-lisp prettyprint-override"><code>(magit-define-command grep (&amp;optional pattern)
    (interactive)
    (let ((pattern (or pattern
                       (read-string "git grep: "
                                    (shell-quote-argument (grep-tag-default))))))
      (with-current-buffer (generate-new-buffer "*Magit Grep*")
        (let ((default-directory (magit-get-top-dir)))
          (insert magit-git-executable " "
                  (mapconcat 'identity magit-git-standard-options " ")
                  " grep -n "
                  (shell-quote-argument pattern) "\n\n")
          (magit-git-insert (list "grep" "--line-number" pattern))
          (grep-mode)
          (pop-to-buffer (current-buffer))))))
  </code></pre>