Spectral-cube

----------------
- Fix `convolve_to` when units are in Jy/beam. Add error/warnings for operations
for all operations that change the spatial resolution for Jy/beam cubes.
- Add ``argmax_world`` and ``argmin_world`` to return the argmin/max position
in WCS coordinates. This is ONLY defined for independent WCS axes
(e.g., spectral) 680
- Bugfix: subcube producing spatial offsets for large images 666
- Switch to using standalone casa-formats-io package for reading in CASA
.image files (this was split out from spectral-cube). 684
- Make it possible to customize ``target_chunksize`` in the CASA reader. 705
- Fix support for dask.distributed. 712
- Bugfix: PhysicalType are now strings. 709

----------------
- Bugfix: subcubes from compound regions previously did not work. 601
- Bugfix: VaryingResolutionSpectralCube.mask_channels now preserves
previous mask. 620
- Refactor tests to use fixtures for accessing data instead of needing to
run a script to generate test files. 598
- Refactor package infrastructure to no longer use astropy-helpers. 599
- Switch to using unified I/O infrastructure from Astropy. 600
- Bugfix: fix slicing of cubes with mask set to None. 621
- Refactor CASA I/O to use dask to access the array/mask data directly
and to use only Python and Numpy to access image metadata. CASA images
can now be read without CASA installed. 607, 609, 613
- Add new dask-friendly classes ``DaskSpectralCube`` and
``DaskVaryingResolutionSpectralCube`` which use dask to efficiently
carry out calculations. 618
- Add new ``statistics`` method on ``DaskSpectralCube`` which allows
several global statistics to be computed by loading each cube chunk
only once. 663

------------------
- Added support for casatools-based io in 541 and beam reading from CASA
images in 543
- Add support for ``update_function`` in the joblib-based job distributor
in 534
- Add tests for WCS equivalence in reprojected images in 589
- Improve error messages when CASA files are read incorrectly in 584
- fix a small bug in matplotlib figure saving in 583
- Allow for reading of beamless cubes in 582
- Add support for 2d world functions in 575 and extrema in 552
- Handle kernels defined as quantities in smoothing in 578
- Fix bug with NPOL header keyword in 576
- Convolution will be skipped if beans are equal-sized in 573
- Fix one-D sliceing with no beam in 568
- Paralellization documentation improvement in 557
- Astropy-helpers updated to 2.0.10 in 553
- Fixed some future warnings in 565
- Added a new documentation example in 548
- Added channel map making capability in 551
- Fix warnings when beam is not defined in 561
- Improvment to joblib parallelization in 564
- Add ppbeam attribute to lower-dimensional objects 549
- Handle CASA file beams in 543 and 545
- Add support for CASA reading using casatools (casa6) in 541
- Bugfix for slicing of different shapes in 532
- Fixes to yt integratino in 531
- Add `unmasked_beams` attribute and change many beams behaviors in 502
- Bugfix for downsampled WCS corners in 525
- Performance enhancement to world extrema in 524
- Simplify conversion from CASA coordsys to FITS-WCS 593
- Add chunked file reading for CASA .image opening 592
- Dropped python 3.5 testing in 592

------------------
- Refactor all beam parameters into mix-in classes; added BaseOneDSpectrum
for common functionality between OneDSpectrum and VaryingResolutionOneDSpectrum.
Retain beam objects when doing arithmetic with LDOs/
(https://github.com/radio-astro-tools/spectral-cube/pull/521)
- Refactor OneDSpectrum objects to include a single beam if they
were produced from a cube with a single beam to enable K<->Jy
conversions
(https://github.com/radio-astro-tools/spectral-cube/pull/510)
- Bugfix: fix compatibility of to_glue with latest versions of glue.
(https://github.com/radio-astro-tools/spectral-cube/pull/491)
- Refactor to use regions instead of pyregion. Adds CRTF support
(https://github.com/radio-astro-tools/spectral-cube/pull/488)
- Direct downsampling tools added, both in-memory and memmap
(https://github.com/radio-astro-tools/spectral-cube/pull/486)

------------------
- Refactor spectral smoothing tools to allow parallelized application *and*
memory mapped output (to avoid loading cube into memory). Created
``apply_function_parallel_spectral`` to make this general. Added
``joblib`` as a dependency.
(https://github.com/radio-astro-tools/spectral-cube/pull/474)
- Bugfix: Reversing a cube's spectral axis should now do something reasonable
instead of unreasonable
(https://github.com/radio-astro-tools/spectral-cube/pull/478)

------------------
- Bugfix and enhancement: handle multiple beams using radio_beam's
multiple-beams feature. This allows `convolve_to` to work when some beams
are masked out. Also removes ``cube_utils.average_beams``, which is now
implemented directly in radio_beam
(https://github.com/radio-astro-tools/spectral-cube/pull/437)
- Added a variety of stacking tools, both for stacking full velocity
cubes of different lines and for stacking full spectra based on
a velocity field (https://github.com/radio-astro-tools/spectral-cube/pull/446,
https://github.com/radio-astro-tools/spectral-cube/pull/453,
https://github.com/radio-astro-tools/spectral-cube/pull/457,
https://github.com/radio-astro-tools/spectral-cube/pull/465)