This allows us to add a docstring to .append() so users can see
the names of the arguments that are being passed, and means we
don't have to remember to prepend run_ when calling a hook.
- The front and back are rendered in one call now. If the front
side contains no custom filters, we can bake {{FrontSide}} into the
rear side. If it did contain custom filters, we return the partially
complete rear template instead, and the calling code can inject
the FrontSide in after it has been fully rendered.
- Instead of modifying "cloze" into something like "cq-2", the card
ordinal and whether we're rendering the question or answer are now
passed in to the rendering filters as context.
- The Rust code doesn't need to support filter names split on '-'
anymore.
- Drop the "Show" part of hint descriptions so i18n support can be
deferred.
- Ignore blank filter names caused by user using two colons instead
of one.
- Fixed hint field and text transposition.
