Named destinations and improved outline interface

There is no support for PDFTeX's outline command yet, but the new one is
much easier to use.

luametalatex-pdf-nametree.lua

@@ -0,0 +1,53 @@
+local min = math.min
+local format = string.format
+local concat = table.concat
+local move = table.move
+local function write(pdf, tree, escaped, step)
+  local nextcount = (#tree-1)//6+1
+  for i=1, nextcount do
+    if #tree > 6 then
+      tree[i] = pdf:indirect(nil, format('<</Limits[%s %s]/Kids[%s 0 R]>>', escaped[step*(i-1)+1], escaped[step*i] or escaped[#escaped], concat(tree, ' 0 R ', 6*i-5, min(#tree, 6*i))))
+    else
+      return pdf:indirect(nil, format('<</Kids[%s 0 R]>>', concat(tree, ' 0 R ', 6*i-5, #tree)))
+    end
+  end
+  move(tree, #tree+1, 2*#tree-nextcount, nextcount+1)
+  return write(pdf, tree, escaped, step*6)
+end
+local function pdf_string(s)
+  -- Emulate other engines here: If  looks like an escaped string, treat it as such. Otherwise, add parenthesis.
+  return s:match("^%(.*%)$") or s:match("^<.*>$") or '(' .. s .. ')'
+end
+local serialized = {}
+return function(values, pdf)
+  local tree = {}
+  for k in next, values do
+    if type(k) ~= "string" then
+      error[[Invalid entry in nametree]] -- Might get ignored in a later version
+    end
+    tree[#tree+1] = k
+  end
+  table.sort(tree)
+  local total = #tree
+  local newtree = {}
+  for i=0,(total-1)//6 do
+    for j=1, 6 do
+      local key = tree[6*i+j]
+      if key then
+        local value = values[key]
+        key = pdf_string(key)
+        tree[6*i+j] = key
+        serialized[2*j-1] = key
+        serialized[2*j] = value
+      else
+        serialized[2*j-1], serialized[2*j] = nil, nil
+      end
+    end
+    if total > 6 then
+      newtree[i+1] = pdf:indirect(nil, format('<</Limits[%s %s]/Names[%s]>>', tree[6*i+1], tree[6*i+6] or tree[total], concat(serialized, ' ')))
+    else
+      return pdf:indirect(nil, format('<</Names[%s]>>', concat(serialized, ' ')))
+    end
+  end
+  return write(pdf, newtree, tree, 36)
+end