Sync reading position with other Twitter apps

[sillygwailo]

This is doable with Tweet Marker, and works in both directions, it looks like (you cat GET the current read mark in Tweet Marker and update Slack's reading position, and you can use Slack's reading position to POST to Tweet Marker).

• https://api.tweetmarker.net/developers/docs
• https://api.slack.com/methods/channels.mark
• https://api.slack.com/events/channel_marked