Support text formatting for Slack

[ta924]

If a command is sent with bold message formatting the logic doesn't seem to match it to a plugin. I would assume this has to do with the formatting of the message being surrounded in * characters. Is there an option to remove formatting or continue to route the message to the plugins if formatting is present?

[fabioxgn]

I guess it have to be handled in this method: https://github.com/go-chat-bot/bot/blob/master/slack/slack.go#L114

It is just passing the message "as is" removing the formatting characters in this method should solve this.