Odtbrain

- BREAKING CHANGES:
- renamed submodule `_preproc` to `_prepare_sino`
- renamed submodule `_postproc` to `_translate_ri`
- missing apple core correction is now applied to the
object function (`f`) instead of the refractive index (`n`),
which is the physically correct approach
- default keyword for `padval` is now "edge"
instead of `None`; the meaning is retained
- enh: added symmetric histogram apple core correction method "sh"
- fix: using "float32" dtype in 3D backpropagation lead to
casting error in numexpr
- enh: improve performance when padding is disabled
- docs: minor update

- feat: basic missing apple core correction (6)
- docs: reordered 3D examples (decreasing importance)

- fix: make phase unwrapping deterministic
- tests: remove one test of the 2D Fourier mapping algorithm due to
instabilities in using scipy.interpolate.griddata
- ref: use `empty_aligned` instead of deprecated `n_byte_align_empty`
- docs: add hint for windows users how to run the 3D examples

- fix: reconstruction volume rotated by 180° due to floating point
inaccuracies (affects `backpropagate_3d_tilted`).

- maintenance release

- enh: employ slice-wise padding to reduce the memory usage (and
possibly the computation time) of
- basic 3D backpropagation algorithm (7)
- 3D backpropagation with a tilted axis of rotation (9)
- ref: replace asserts with raises (8)
- ref: multiprocessing-based rotation does not anymore require
a variable (_shared_array) at the top level of the module; As a
result, multiprocessing-rotation should now also work on Windows.