Add CHANGELOG.md + Upgrading notes

Author: ericproulx

CHANGELOG.md

@@ -11,6 +11,7 @@
 * [#2549](https://github.com/ruby-grape/grape/pull/2549): Delegate cookies management to `Grape::Request` - [@ericproulx](https://github.com/ericproulx).
 * [#2554](https://github.com/ruby-grape/grape/pull/2554): Remove `Grape::Http::Headers` and `Grape::Util::Lazy::Object` - [@ericproulx](https://github.com/ericproulx).
 * [#2556](https://github.com/ruby-grape/grape/pull/2556): Remove unused `Grape::Request::DEFAULT_PARAMS_BUILDER` constant - [@eriklovmo](https://github.com/eriklovmo).
+* [#2561](https://github.com/ruby-grape/grape/pull/2561): Optimize hash alloc for middleware's default options - [@ericproulx](https://github.com/ericproulx).
 * Your contribution here.
 
 #### Fixes

UPGRADING.md

@@ -3,6 +3,11 @@ Upgrading Grape
 
 ### Upgrading to >= 2.4.0
 
+#### Grape::Middleware::Base
+
+- Second argument `options` is now a double splat (**) instead of single splat (*). If you're redefining `initialize` in your middleware and/or calling `super` in it, you might have to adapt the signature and the `super` call. Also, you might have to remove `{}` if you're pass `options` as a literal `Hash` or add `**` if you're using a variable.
+- `Grape::Middleware::Helpers` has been removed. The equivalent method `context` is now part of `Grape::Middleware::Base`.
+
 #### Grape::Http::Headers, Grape::Util::Lazy::Object
 
 Both have been removed. See [2554](https://github.com/ruby-grape/grape/pull/2554).