Update changelog for v3.0.0

[jkowens]

I went ahead and dispensed with the unstable branch because it was causing confusion. I tagged v2.2.0 and moved on to master being for v3.0. Time to start moving forward 😅

If someone can help update the changelog with details about 3.0 that would be appreciated.

Hopefully we can get a core team member that can cut releases to do that for 2.2.0 and then 3.0 at some point.

If anyone needs to pin their Gemfile to v2.2.0 they can do:

gem 'sinatra', git: 'https://github.com/sinatra/sinatra.git', tag: 'v2.2.0'

cc: @sinatra/sinatras-helpers @sinatra/team-sinatra

[dentarg]

Hmm... @namusyaka seems to be working on v2.1.1 and #1676 was just merged to master.

@namusyaka did you see this issue? I think it would be good if you can do what @jkowens suggest and release v2.2.0 from https://github.com/sinatra/sinatra/releases/tag/v2.2.0 to avoid any further confusion.

[namusyaka]

Oops I overlooked this. Thanks for letting me know.