Add documentation for public API endpoints

[RAnders00]

Third-party applications, bots, websites etc. often find the need to integrate with BetterTTV, and in the past they've used the v2 API for that with great success.

It would be great to hear:

• When the old (https://api.betterttv.net/2/) API is being deprecated, and when it will be removed,
• and what endpoints of the new API (https://api.betterttv.net/3/) third-party devs are supposed and allowed to be used

I'm mostly looking at /cached/users/twitch/:channelID and /cached/emotes/global in my applications.

It would be great to have a .md file in this repository, or a page on the website to link to, as a reference for the v3 API, if that was possible, and maybe some guidelines for consuming and implementing against the API.

[night]

Currently we don't provide maintenance/support for usage of our API in other applications, which is why we don't document our APIs. Using any of our APIs is currently at your own risk, and could break/change at any time (though that's not something we try to do, hence versioning).

v2 will be removed soon, but there are still some internal services using v2 (which is the only reason it remains online).

While we still don't officially support v3, you could consider the endpoints used within our extension to be deemed as safer to use (which are the cached ones you noted).

[makedir]

@night Because my ticket was closed/moved, I am asking here again:

https://api.betterttv.net/3/
global: https://api.betterttv.net/3/cached/emotes/global
badges: https://api.betterttv.net/3/cached/badges
bttv channel emotes: https://api.betterttv.net/3/cached/users/twitch/121059319
ffz channel emotes: https://api.betterttv.net/3/cached/frankerfacez/users/twitch/121059319
changelog: https://api.betterttv.net/3/cached/changelog

All gone. The v4 api was working some weeks ago, and now it isnt anymore. It just redirects to https://betterttv.com/ instead of giving an json output.

[night]

requests appear to succeed normally for the links specified:

curl https://api.betterttv.net/3/cached/users/twitch/121059319 --head
HTTP/2 200 

[Nerixyz]

requests appear to succeed normally for the links specified:

I suppose they're setting Sec-Fetch-Mode: navigate (When navigating to the URL in the browser, MDN docs):

curl "https://api.betterttv.net/3/cached/users/twitch/121059319" -H "Sec-Fetch-Mode: navigate" --head
HTTP/1.1 302 Moved Temporarily

[makedir]

Weird... There was a change made to the API though, in the past 1-3 weeks. It seems to not send back jsons for some headers? That seems to be changed. I was not getting API feedback the other day in my app, but I just tested it this moment, and it seems to work again. Do you need to pass some specific header information for the API to work which was changed? If you open the API end points in a browser, it redirects to https://betterttv.com/. That was still working a few weeks ago.