[MRG + 1] Convert filename to lowercase to check for extension (#169)

* Creates a new variable that stores a lowercase version of the filename

* Remove variable

camelot/handlers.py

@@ -26,7 +26,7 @@ class PDFHandler(object):
     """
     def __init__(self, filename, pages='1'):
         self.filename = filename
-        if not self.filename.endswith('.pdf'):
+        if not filename.lower().endswith('.pdf'):
             raise NotImplementedError("File format not supported")
         self.pages = self._get_pages(self.filename, pages)