support for auto-numbering of lists

[metronome12]

In markdown I can create a number list like this:

1. item 1
1. item 2
1. item 3

and it will auto number them like this

1. item 1
2. item 2
3. item 3

It would be good to provide that in MarkdownUI

[gonzalezreal]

MarkdownUI 2.x is compatible with the GitHub Flavored Markdown spec, which includes the CommonMark spec and, thus, the auto-numbering lists feature. You can see this in the companion demo project under the Lists screen in the Customization Example section:

swift-markdown-ui/Examples/Demo/Demo/ListsView.swift

Lines 68 to 70 in fdc444d

	10. James Madison
	1. James Monroe
	1. John Quincy Adams

In the example, there is an auto-numbered list that starts at 10 and is styled with roman numbers.

Please, check the demo project and the docs to get acquainted with all the library features.