Collect page names for the sitemap as HTML pages are built.

def html_page_context(app, pagename, templatename, context, doctree):
    ''' Collect page names for the sitemap as HTML pages are built.

    '''
    site = context['SITEMAP_BASE_URL']
    version = context['version']
    app.sitemap_links.add(site + version + '/' + pagename + ".html")