added mark down to html in chat message

[iamajeesh]

Mark down added to convert markdown chat message text to HTML example, Hi to Hi.

[Pustur]

We had some discussion for this sort of thing here, feel free to give it a read:
Pustur/whatsapp-chat-parser#251

I think this feature is cool to have, but i don't want to overcomplicate things too much.

To recap i'd accept a PR only if it does the following:

• Uses an established library to parse markdown-like syntax (I don't trust regex for this)
• Only transforms the styles documented here and nothing more: How to format your messages | WhatsApp Help Center

Your current implementation breaks the links created by react-linkify by the way 😔