Documentation and changelog are out of date

[Marti Raudsepp]

Documentation on readthedocs displays 2.4.0 as the last release, that's two releases behind:

• https://django-celery-results.readthedocs.io/en/latest/index.html
• https://django-celery-results.readthedocs.io/en/latest/changelog.html

There is also an old similar issue, but it seems like it got fixed back then:

• #279

[suspiciousRaccoon]

This is still an issue. There are several links that are broken.