Better --- horizontal rule support

Markdown editors use --- for defining a horizontal rule:

• GitHub
• Typora
• Marktext

and many more.

At indiehackers, you only support ----, which is not consistent with the spec. In addition, horizontal rules on indiehackers only work in posts, not comments.

Please become spec compliant and add full support for horizontal rules. These changes will help with discoverability and the writing experience.

Thanks!