Both crates have been deprecated in favour of `nannou_egui` and have
moved into a separate repository:

https://github.com/nannou-org/nannou_conrod

See the following issue for some context on the motivations behind
switching to nannou_egui:

https://github.com/PistonDevelopers/conrod/issues/1454

See the following PR for the merge of `nannou_egui` into the main nannou
repository:

https://github.com/nannou-org/nannou/pull/854

Conrod-specific examples have been moved to the separate `nannou_conrod`
repo, while other examples that used `nannou_conrod` have been
transitioned use `nannou_egui`.