Don't override unordered (bulleted) list symbols

[Ali Servet Donmez]

Markdown syntax allows either *, -, or + for unordered (bulleted) lists, but markdownfmt will override * or + with -s.

I think it is for the best if you'd stick to the user's personal preference.

[Ali Servet Donmez]

D–Oh! I should've created this issue at https://github.com/shurcooL/markdownfmt instead. Closing in favor of shurcooL/markdownfmt#6.

[Dmitri Shuralyov]

Thanks.