Text.Pandoc.Lua: respect metatable when getting filters

This change makes it possible to define a catch-all function using lua's
metatable lookup functionality.

    function catch_all(el)
      …
    end

    return {
      setmetatable({}, {__index = function(_) return catch_all end})
    }

A further effect of this change is that the map with filter functions
now only contains functions corresponding to AST element constructors.

0 files changed, 0 insertions, 0 deletions