[WIP] adds timeline requests

[thoraxe]

I make extensive use of the timeline endpoint: https://developer.twitter.com/en/docs/twitter-api/tweets/timelines/api-reference/get-users-id-tweets

I had already built up a bunch of code in a library but using a gem that the community is pointing to would be beneficial.

Hopefully, this code is acceptable. Let me know if you want any changes. Tweets and Mentions are separate endpoints under the "timeline" umbrella, so if you'd prefer a reorganization here, I'm all for it.

[julianfssen]

Hey, @thoraxe ! Thanks for the PR! 😁

The code looks good to me and I'm fine with the code organization. We're currently using this gem in production and looking to restructure it a bit, similar to how you're already doing here with Tweetkit::Client::Timeline so it's all good!

I'll be merging the PR soon together with another open PR, and I'll let you know when that's done.

Thanks for trying out the gem and contributing @thoraxe ! Appreciate the help 😁