[docmaker] Allow `foo[bar]' as identifier. We need this to handle equally named properties in different modules. * src/tools/docmaker/content.py (re_identifier), src/tools/docmaker/sources.py (re_crossref): Allow `foo[bar]'. * src/tools/docmaker/tohtml.py (HtmlFormatter::make_html_word, HtmlFormatter::index_exit, HtmlFormatter::section_enter, HtmlFormatter::block_enter): Handle `foo[bar]'.