Close bullet list after hitting enter on empty list line

[Calamari]

Since I like this convenience on every markdown editor I go, I thought I add this here too. This adds the following behavior:

Hitting enter on empty list rows, will close the (numbered) bullet list.

Here an example:

When having the following content in a textarea (| is representing the caret):

- list 1
- |

something more...

After hitting enter the content will now look like this:

- list 1

|

something more...

instead of this:

- list 1
- 
- |

something more...

I added the same for numbered bullet lists.

As a bonus, I also fixed the bug, that hitting enter on a line like 9. will misplace the caret about one character, since the length of the old number was used, instead of the added 10..

Note about testing:

Since there are no tests in this repository, I tested all the cases I could come up with manually.

If something is missing, or you want to have something changed. I am eager to do it. I would like to have this feature in. :)