v0.4.0

What's Changed

• Add tests for visual overpass for Cape Town and Envisat by @samtx in #30
• Remove requirements files, specify optional dependencies in setup.py by @samtx in #36
• Add Observer.pass_list() method to directly return a list of overpass… by @samtx in #39
• Remove zoneinfo.py and replace with standard importerror checking in … by @samtx in #40
• Refactor cache objects by @samtx in #41
• Add better help text to CLI by @samtx in #42
• Add tests to confirm that CLI works without arguments by @samtx in #43
• Update Celestrak source to use new GP url by @samtx in #44

Full Changelog: v0.3.0...v0.4.0