Lua filters: preload text module (#4077)

The `text` module is preloaded in lua. The module contains some UTF-8
aware string functions, implemented in Haskell.  The module is loaded on
request only, e.g.:

    text = require 'text'
    function Str (s)
      s.text = text.upper(s.text)
      return s
    end

1 files changed, 9 insertions, 0 deletions

diff --git a/test/lua/uppercase-header.lua b/test/lua/uppercase-header.lua
new file mode 100644
index 000000000..8e86911c0
--- /dev/null
+++ b/test/lua/uppercase-header.lua
@@ -0,0 +1,9 @@
+local text = require 'text'
+
+local function str_to_uppercase (s)
+  return pandoc.Str(text.upper(s.text))
+end
+
+function Header (el)
+  return pandoc.walk_block(el, {Str = str_to_uppercase})
+end