This is probably one of the reasons you are here in the first place. Gitter supports markdown in chat. Yes, that's right. Markdown. In Chat. Such win.
We not only support basic markdown, but also we do syntax highlighting for code and also support issue mentions and @ mentions.
For those unfamiliar with markdown, please find this pretty simple reference below for your pleasure and enjoyment. You can access a similar guide in the Gitter application by clicking on the icon to the right of the chat input area. It looks like this: