`._get_compiled_doc` memoizes in `._doc` yet is called in different conditions

[o-jasper]

_generate_html_toc adds libmarkdown.MKD_TOC to .flags, so differing from the other ones that call _get_compiled_doc. I am not sure what the effect of changing .flags is.

Since the memoized value is invalidated want to

if self.flags &libmarkdown.MKD_TOC ==0: delattr(self, '_doc')