v1.2.3

Changed

• Consolidated optional 'browsify' and 'desktop_image' dependencies into simply
  'pillow'.
• Any attempt to use functionality that requires an optional dependency now raises
  a ModuleNotFoundError naming the required module.
  • To support this, astropy objects are now always imported through
    loaders.astrowrap.
• Updates to documentation to include instructions for pip users, etc.

Fixed

• docs/index.md updated to reflect the same content as README.md

Removed

• Experimental save_sparklines() function in pdr.browsify, and along with
  it, the optional matplotlib dependency.
• Unnecessary full matplotlib dependency for Notebook use.

Full Changelog: v1.2.2...v1.2.3