Handling of nested ordered list

Hi

First to everyone who's contributed to this code, or pays for/assists with the hosting - thanks! its an awesome tool.

So,

If I'm using the editor and I start a list like so:

```
1. An Item
```
then hit return, I get (as expected):

```
1. An Item
2.
```

But, if I'm in a nest like so:

```
1. An Item
2. Another Item
3.
```
Then hit tab to indent item, the `3.` indents, but doesn't reset to be `1` (effectively `2.1`) which would be handy, versus going back to start of line, spacing 4 spaces then replacing the 3 with a 1, from which point the automatic numbering works correctly again within the list.

Similarly, it'd be great if shit tabbing from the last item on a nested list back into its parent list at the correct number.