New
* Replace `pybind11` as a build dependency with `numpy`.
* Generate ABI3 wheels.
Changed
* Remove `cython` leftovers.
* Add minimum versions to most dependencies.
* Always compile with C++11 as we don't use any newer features.
* Bump the minimum qmflows version to >= 1.12.1.
* Increase the SCF convergence in the (non-guess) templates from 5e-04 to 1e-06.
Fixed
* Fix the ill-defined active space for unrestricted calculations.