V1.7.0

Bug Fixes

• Fixed spectral_slab crashing when spectral_axis has unit of pixels and
  the bounds are also defined in the unit of pixels. [#926]

• Fixed resulting spectral_axis containing NaN when a cube is passed into
  Spectrum1D without WCS nor spectral axis and the spatial-spatial dimension
  is smaller than spectral dimension. [#926]

• Fixed WCS not accurately reflecting the updated spectral axis after slicing a
  Spectrum1D. [#918]

Other Changes and Additions

• Logger usage is removed. Warnings now issued using Python warnings module.
  This enables more granular warning control for downstream packages. [#922]