title: Parsing url html with lxml failed loading foreign entity
body: <p>I'm trying to parse through the emojis in the url provided.  It's a tutorial in Data Wrangling Book to help me understand data analysis.  This is a verbatim code from the text book and gives me the error at the end.  I have heard suggestions for using urllib2 but the point of this exercise is to use lxml.  Is this achievable, or is this example just outdated?  Can you provide some insight to get this to run, parse the emojis, and then return the list.</p>
  
  <pre><code>from lxml import html
  
  page = html.parse('http://www.emoji-cheat-sheet.com/')
  
  proper_headers = page.xpath('//h2|//h3')
  proper_lists = page.xpath('//ul')
  
  all_emoji = []
  
  for header, list_cont in zip(proper_headers, proper_lists):
      section = header.text
      for li in list_cont.getchildren():
          emoji_dict = {}
          spans = li.xpath('div/span')
          if len(spans):
              link = spans[0].get('data-src')
              if link:
                  emoji_dict['emoji_link'] = li.base_url + link
              else:
                  emoji_dict['emoji_link'] = None
              emoji_dict['emoji_handle'] = spans[1].text_content()
          else:
              emoji_dict['emoji_link'] = None
              emoji_dict['emoji_handle'] = li.xpath('div')[0].text_content()
          emoji_dict['section'] = section
          all_emoji.append(emoji_dict)
  
  print all_emoji
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "chp11-scraping/lxml_emoji_xpath.py", line 24, in &lt;module&gt;
      page = html.parse('http://www.emoji-cheat-sheet.com/')
    File "/home/ryan/.local/lib/python2.7/site-packages/lxml/html/__init__.py", line 940, in parse
      return etree.parse(filename_or_url, parser, base_url=base_url, **kw)
    File "src/lxml/etree.pyx", line 3426, in lxml.etree.parse
    File "src/lxml/parser.pxi", line 1840, in lxml.etree._parseDocument
    File "src/lxml/parser.pxi", line 1866, in lxml.etree._parseDocumentFromURL
    File "src/lxml/parser.pxi", line 1770, in lxml.etree._parseDocFromFile
    File "src/lxml/parser.pxi", line 1163, in lxml.etree._BaseParser._parseDocFromFile
    File "src/lxml/parser.pxi", line 601, in lxml.etree._ParserContext._handleParseResultDoc
    File "src/lxml/parser.pxi", line 711, in lxml.etree._handleParseResult
    File "src/lxml/parser.pxi", line 638, in lxml.etree._raiseParseError
  IOError: Error reading file 'http://www.emoji-cheat-sheet.com/': failed to load external entity "http://www.emoji-cheat-sheet.com/"
  </code></pre>