templater: factor out helper that renders named template as string
This is quite common in non-web templating, and **kwargs expansion is annoying
because of the unicode-ness of Python3.
templater: rename .render(mapping) to .renderdefault(mapping) (API)
I'm going to add templ.render(t, mapping) and templ.generate(t, mapping) in
place of stringify(templ(t, **mapping)) and templ(t, **mapping) respectively.
.. api::
The ``render(mapping)`` method of the templater has been renamed to
``renderdefault(mapping)``.
templater: fix invalid reference of runsymbol in doctest
Oversight at
da710c3df4dc. I was just lucky that this lambda function is
never evaluated.