Join takes a slice of mentions, and joins them using the sep.

Parse takes the message text, and the channel ID where the message was sent, and parses the mentions in the message.

ParseAndSplice calls Parse(), and uses the start/end index of each mention to remove it from the message and return the resulting string.

TypeChannel is for @channel mentions.

TypeChannelRef is a reference to another channel in a message, like if a user were to type "join #general".

TypeEveryone is for @everyone metnions.

TypeGroup represents a workspace group mention.

TypeHere is for @here mentions.

TypeUser represents a user mention.

Mention represents a Slack message mention.

Type is a faux-enum for describing whether it was a user or group mention.