title: DOMPDF - memory leak issue
body: <p>I am using DOMPDF 0.6.0 beta 3. I got this php error when the system generating many pdf. </p>
  
  <p>PHP Fatal error:  Allowed memory size of 268435456 bytes exhausted (tried to allocate 639 bytes) in /home/deal4uco/public_html/lib/dompdf/lib/php-font-lib/classes/font_binary_stream.cls.php on line 144</p>
  
  <p>The font file is big. Almost 24MB+. I believe the dompdf have made it as cache (1.5M+). I don't think the memory issue is related with font file.</p>
  
  <p>Can i know what the problem cause it? Many people said the html contant cannot include these html tag (table, tr, td). Is it really that cause the above issue?</p>