Changes:
Fixed a bug that caused the wrong character encoding to be used
when checking multiple documents with different character encodings
Added support for proxies when validating remote documents
Added support for validation of URIs. Thanks to Ville Skyttä for
the patch.
Updated DTDs XHTML 1.0 Second Edition and added support for XHTML
1.1, MathML2 2.0, WML 1.3, 1.2, 1.1, and 1.0.
* added a --emacs command-line option to produce output intended
for parsing by Emacs
* added errors for references to non-existent IDs in attributes
such as the headers attribute of the td element