Sphinx Pygments lexer filter extension?
===

I have a Lisp-like language I would like to highlight using Pygments in Sphinx code snippet documentation.  My approach is to extend the existing CommonLispLexer to add the built-in names using a NameHighlightFilter.  However, it is not working, so I must be missing something obvious.  I have added the following to my conf.py:

    def setup(app): 
        from sphinx.highlighting import lexers
        from pygments.lexers import CommonLispLexer
        from pygments.token import Name
        from pygments.filters import NameHighlightFilter
        tl_lexer = CommonLispLexer()
        tl_lexer.add_filter(NameHighlightFilter(
                names=['define-function', 'define-macro', 
                       'define-variable', 'define-constant'],
                tokentype=Name.Builtin,
                ))
        app.add_lexer('tl', tl_lexer)

    highlight_language = 'tl'

But the NameHighlightFilter has no effect.  Code blocks are highlighted as if they were Lisp, but my new builtin names have no special highlighting.

