This is a full revert of release 3.5.0.

3.5.0 contained multiple backwards-incompatible (BC) breakages that were not
supposed to be released in a minor version, and therefore had to be reverted.

Due to unfortunate branch naming issues when migrating from the old develop
branch, develop was renamed 3.5.x, but contained multiple BC breaks that
were fundamentally incompatible with the 3.0.0 and newer features.

Thanks to @fabiang for promptly detecting the issue and reporting it
at #59