Breaking Changes
* The `gftool.pade` module had a minor rework.
The behavior of filters changed. Future breaking changes are to be expected,
the module is not well-structured.
New Features
* add `gftool.lattice.onedim` for Green's function of one-dimensional lattice
* add fitting of high-frequency moment to `gftool.fourier.iw2tau` (e2c92e2)
Other New Features
* add `gftool.pade_frequencies` (9f492fc)
* add `gftool.density_iw` function as common interface to calculate occupation
number from Matsubara or Padé frequencies
* allow calculation of `gftool.lattice.bethe` for Bethe lattice at complex points
(note, that this is probably not a physically meaningful quantity) (ccbac7b)
* add stress tensor transformation `gftool.lattice.square.stress_trafo` for 2D (528fb21)
Bug fixes
* Fix constant in `gftool.fourier.tau2iw_ft_lin` (e2163e3).
This error most likely didn't significantly affect any results for a reasonable
number of tau-points.
* `gftool.density` should work now with gu-style matrices (4deffdf)
Documentation
* Functions exposed at the top level (`gftool`) should now properly appear in
the documentation.