LuaJIT compatibility

Spoiler alert: Anselme run ~1.5x slower in LuaJIT than Lua 5.3/5.4. I didn't expected LuaJIT to be able to optimize anything with my super performant and cache friendly AST walker interpreter, but being this much slower is kinda impressive.

parser/Source.lua

@@ -1,4 +1,5 @@
 local class = require("class")
+local utf8 = utf8 or require("lua-utf8")
 
 local Source
 Source = class {

parser/code_to_tree.lua

@@ -1,5 +1,7 @@
 --- transform raw code string into a nested tree of lines
 
+local utf8 = utf8 or require("lua-utf8")
+
 local Source = require("parser.Source")
 
 local function indented_to_tree(indented)

parser/expression/comment.lua

@@ -30,7 +30,7 @@ comment = primary {
 				subcomment, rem = comment:parse(source, rem, limit_pattern)
 
 				table.insert(content_list, "((")
-				for _, c in ipairs(subcomment) do table.insert(content_list, c) end
+				table.insert(content_list, subcomment)
 				table.insert(content_list, "))")
 			-- no end token after the comment
 			elseif not rem:match("^%)%)") then