chunk up the saved file to be git friendly

Now we don't save a bunch of irrelevant fields from editor buffers, just
lines.

The cost: autosave every 3 seconds becomes much more expensive.

0010-initialize_editor

@@ -3,6 +3,7 @@ initialize_editor = function(obj)
 		local scaled_fontsize = scale(20)
 		local scaled_lineheight = math.floor(scaled_fontsize*1.3)
 		obj.editor = edit.initialize_state(vy(obj.y), math.floor(vx(obj.x)), math.ceil(vx(obj.x+obj.w)), scaled_fontsize, scaled_lineheight)
+		obj.editor.lines = load_array(obj.data)
 		Text.redraw_all(obj.editor)
 	end
 end

0062-save_graph_to_disk

@@ -1,5 +1,27 @@
 save_graph_to_disk = function()
+	local data = {next=First_available_id}
+	-- save a copy of Nodes with various fields deleted
+	local kvs = {}
+	for k,v in pairs(Nodes) do
+		v = table.copy(v)
+		v.data = {}
+		for i,l in ipairs(v.editor.lines) do
+			table.insert(v.data, l.data)
+		end
+		v.editor = nil
+		table.insert(kvs, {k, v})
+	end
+	-- sort the copy to avoid spurious diffs in version control
+	table.sort(kvs, function(a, b) return a[1] < b[1] end)
+	data.nodes = Nodes
 	local f = App.open_for_writing(Filename)
-	f:write(json.encode({next=First_available_id, nodes=Nodes}))
+	f:write('{ "next" : '..First_available_id..', "nodes" : {\n')
+	for i,kv in ipairs(kvs) do
+		if i > 1 then
+			f:write(',')
+		end
+		f:write('"'..kv[1]..'": '..json.encode(kv[2])..'\n')
+	end
+	f:write('}}\n')
 	f:close()
-end
+end

0063-load_graph_from_disk

@@ -4,4 +4,4 @@ load_graph_from_disk = function()
 	f:close()
 	Nodes = data.nodes or {}
 	First_available_id = data.next
-end
+end

0068-table.copy

@@ -0,0 +1,7 @@
+table.copy = function(h)
+	local result = {}
+	for k,v in pairs(h) do
+		result[k] = v
+	end
+	return result
+end