:bookmark: Changelog entry for v0.3.0

[weiji14]

:tada: Third minor release of zen3geo.

Preview at https://zen3geo--41.org.readthedocs.build/en/41/changelog.html

Previous changelog at #27.

Changelog made by following these steps:

1. Copy draft release note from https://github.com/weiji14/zen3geo/releases and paste it into docs/changelog.md
2. Use emojize.py script from https://stackoverflow.com/questions/42087466/sphinx-extension-to-use-github-markdown-emoji-in-sphinx to convert GitHub Markdown emojis like :boom: to :boom:
   • E.g. run python docs/emojize.py docs/changelog.md > docs/changelog.md2
3. Pick some highlight items

This is a simplified version of PyGMT's release process at https://www.pygmt.org/v0.7.0/maintenance.html#making-a-release

Relates to #38.