Release v0.2.1

What's Changed

• Update README.md by @elshize in #23
• Update README by @elshize in #24
• Bugfix for header stats by @JMMackenzie in #25
• Update CI by @elshize in #26
• Small refactoring + tests by @elshize in #27
• Implement RandomAccessBinaryCollection by @elshize in #30
• Implement payload vector & slice by @elshize in #31
• Add ability to write lexicons directly by @JMMackenzie in #32

Full Changelog: v0.1.1...v0.2.1