title: &nbsp text not handled by the lxml
body: <p>My html file has the following line </p>
  
  <pre><code>&lt;tr&gt;&lt;td&gt;$nbsp;&lt;/td&gt;&lt;tr&gt; 
  </code></pre>
  
  <p>But when I do the parsing with lxml:</p>
  
  <pre><code>from lxml import tree as ET
  tree = ET.parse("file.html")
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>Traceback (most recent call last):
  File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  File "lxml.etree.pyx", line 3310, in lxml.etree.parse (src/lxml/lxml.etree.c:72517)
  File "parser.pxi", line 1791, in lxml.etree._parseDocument (src/lxml/lxml.etree.c:105979)
  File "parser.pxi", line 1817, in lxml.etree._parseDocumentFromURL (src/lxml/lxml.etree.c:106278)
  File "parser.pxi", line 1721, in lxml.etree._parseDocFromFile (src/lxml/lxml.etree.c:105277)
  File "parser.pxi", line 1122, in lxml.etree._BaseParser._parseDocFromFile (src/lxml/lxml.etree.c:100227)
  File "parser.pxi", line 580, in lxml.etree._ParserContext._handleParseResultDoc (src/lxml/lxml.etree.c:94350)
  File "parser.pxi", line 690, in lxml.etree._handleParseResult (src/lxml/lxml.etree.c:95786)
  File "parser.pxi", line 620, in lxml.etree._raiseParseError (src/lxml/lxml.etree.c:94853)
  lxml.etree.XMLSyntaxError: Entity 'nbsp' not defined, line 14, column 159
  </code></pre>