Improve highlither for document edits

The syntax highlighter keep a cache of the documents like tokenization.

In order to minimize the amount of tokenize re-computations we insert some
emtty lines or remove some lines in the highlither lines corresponding to
the lines added or removed to the document.

data/core/doc/highlighter.lua

@@ -44,12 +44,25 @@ function Highlighter:reset()
   self.max_wanted_line = 0
 end
 
-
 function Highlighter:invalidate(idx)
   self.first_invalid_line = math.min(self.first_invalid_line, idx)
   self.max_wanted_line = math.min(self.max_wanted_line, #self.doc.lines)
 end
 
+function Highlighter:insert_notify(line, n)
+  self:invalidate(line)
+  for i = 1, n do
+    table.insert(self.lines, line, nil)
+  end
+end
+
+function Highlighter:remove_notify(line, n)
+  self:invalidate(line)
+  for i = 1, n do
+    table.remove(self.lines, line)
+  end
+end
+
 
 function Highlighter:tokenize_line(idx, state)
   local res = {}

data/core/doc/init.lua

@@ -348,7 +348,7 @@ function Doc:raw_insert(line, col, text, undo_stack, time)
   push_undo(undo_stack, time, "remove", line, col, line2, col2)
 
   -- update highlighter and assure selection is in bounds
-  self.highlighter:invalidate(line)
+  self.highlighter:insert_notify(line, #lines - 1)
   self:sanitize_selection()
 end
 
@@ -375,7 +375,7 @@ function Doc:raw_remove(line1, col1, line2, col2, undo_stack, time)
   end
 
   -- update highlighter and assure selection is in bounds
-  self.highlighter:invalidate(line1)
+  self.highlighter:remove_notify(line1, line2 - line1)
   self:sanitize_selection()
 end