Add percent (%) to _unquotedChars in RDFa 1.1. parser

If the percent (%) character appears in a URI, the parser should not quote it, as this will lead to double quoted URIs that will no longer resolve. 

For instance:

The HTML page at :

<http://link.springer.com/chapter/10.1007%2F978-3-642-25093-4_9>

contains a link to an image:

<http://link.springer.com/static-content/lookinside/613/chp%253A10.1007%252F978-3-642-25093-4_9/000.png>

which becomes:

<http://link.springer.com/static-content/lookinside/613/chp%25253A10.1007%25252F978-3-642-25093-4_9/000.png>

in the resulting RDF graph. 

Adding the percent character to the _unquotedChars should fix this.