v0.3

What's Changed

• Comet corrections, #485, #491 by @astronomerritt in #502
• Small issues: #499, #498, #489, #488 by @astronomerritt in #503
• Initial scaffolding commit for plugable cometary activity models. by @drewoldag in #504
• Adding conditional back. by @drewoldag in #506

Full Changelog: v0.2...v0.3