title: scrapy log issue
body: <p>i have multiple spiders in one project , problem is right now i am defining <strong>LOG_FILE</strong> in SETTINGS like </p>
  
  <pre><code>LOG_FILE = "scrapy_%s.log" % datetime.now()
  </code></pre>
  
  <p>what i want is <code>scrapy_SPIDERNAME_DATETIME</code></p>
  
  <p>but i am unable to provide spidername in log_file name ..</p>
  
  <p>i found </p>
  
  <pre><code>scrapy.log.start(logfile=None, loglevel=None, logstdout=None)
  </code></pre>
  
  <p>and called it in each spider <strong>init</strong> method but its not working ..</p>
  
  <p>any help would be appreciated </p>