Update the `Key Features` in README.md

Get release 4.2.0 ready.

Merge pull request IBAnimatable#475 from IBAnimatable/feature/get-4-1…

…-ready

Get release 4.1.0 ready

Merge pull request IBAnimatable#454 from IBAnimatable/feature/release…

…_400

Bump 4.0.0

Add contributor to the CHANGELOG.md

Get release 3.1.2 ready.

Prepare for release 3.1.1

Merge pull request IBAnimatable#361 from IBAnimatable/hotfix/swiftlint

Bump swiftlint 0.13.0

Merge pull request IBAnimatable#353 from IBAnimatable/feature/get-rel…

…ease-3.0.1-ready

Get release 3.0.1 ready.

Merge pull request IBAnimatable#352 from IBAnimatable/feature/get-rel…

…ease-2.8.2-ready

Get release 2.8.2 ready.