docs(changelog): add changelog for 4.0.0-beta.4

docs(changelog): add changelog for 2.4.4

docs(changelog): add changelog for 4.0.0-beta.3

docs(changelog): add changelog for 2.4.3

docs(changelog): release notes for 4.0.0-beta.2

docs(changelog): add release notes for 2.4.2

docs(changelog): add changelog for 4.0.0-beta.1

docs(changelog): add changelog for 2.4.1

docs(changelog): add changelog for 2.4.0

feat: update to rxjs@5.0.1 and unpin the rxjs peerDeps via ^5.0.1 (an…

…gular#13572)

Now that rxjs is stable and the rxjs team follows semver, we can update and unpin the dependency safely.

From now on the Angular application/library developers are in charge of controlling the rxjs version as long as it's newer than 5.0.1.

closes angular#13561
closes angular#13478
closes angular#13572