dust_extinction: Interstellar Dust Extinction Models

What's Changed Logo by @karllark in https://github.com/karllark/dust_extinction/pull/254 Add utility to save G23 model to ascii files by @karllark in https://github.com/karllark/dust_extinction/pull/259 Updated optical-NIR anchor wavelengths for G24 SMC models by @RanitBehera in https://github.com/karllark/dust_extinction/pull/261 Add KP5 as a grain model by @keflavich in https://github.com/karllark/dust_extinction/pull/258 upating G25 -> G26 by @karllark in https://github.com/karllark/dust_extinction/pull/263 Fix the P92 test error by @karllark in https://github.com/karllark/dust_extinction/pull/266 Add documentation on curve normalization by @karllark in https://github.com/karllark/dust_extinction/pull/265 New Contributors @RanitBehera made their first contribution in https://github.com/karllark/dust_extinction/pull/261 Full Changelog: https://github.com/karllark/dust_extinction/compare/v1.6...v1.7