Mixed type lists

[RhvdG]

I'd like to see support for mixed type lists, like so:

1. Item
    a. Sub-item
    b. Sub-item
        • Sub-sub-item

Ideally, of course, within one list the type should auto-continue based on ident level, and we'd be able to use Roman (upper and lower case) and Arabic numerals, upper and lower case letters, and bullets (and maybe even more), without a prescribed order/level (just adapt to whatever user picks).