- Reduce environment pollution with a separate $bin output containing programs,
plugins, and shared data. Libraries remain in $out and are not installed into
the environment.
- Only propagate build inputs as required.
Instead of one package `extra-cmake-modules`, there is now `ecm` and
`ecmNoHooks`. The latter is used when one does not want to incur a Qt 5
dependency; it is also available as a top-level package
`extra-cmake-modules`.
