[opinionated] Prefer emitting hyphen `-` over asterisk `*` for unordered list markup

[zm-cttae]

Currently this package uses *. This works but goes against Markdown conventions of using - which might be because * usually means italics.
In an ideal world the editor would emit - for unordered lists. * is also a little too much like RST and MediaWiki.

[wayjake]

I agree!

These three settings seem to get this package up to date with most modern standards that I run into these days:

{ headingStyle: 'atx', bulletListMarker: '-', emDelimiter: '*' }