add options for list & hr output

[af4jm]

added options, with current behavior as default, for formatting lists & HRs... for example, I could then add this to my options...

{
    "hr": '---',
    "bullets": '-',
    "indent": 4
}

to have sublists indented 4 spaces instead of 2 and to have all ULs use - regardless of level... thus I can set Breakdance to output in compliance with my .markdownlintrc