The v0.3.0 Release

A bunch of big changes:

• entire codebase is now mypy type-checked, with runtime type enforcement so that a bug doesn't lead to malformed indexes being written to disk
• all disk writes are now atomic so that power loss / SIGTERM during execution doesn't leave the index in an inconsistent state (as long as the archive folder is on a local, non-network filesystem)
• core data model now uses typed, immutable dataclasses instead of plain dicts
• schema and json loading and parsing are formalized all in one place schema.py (laying the foundations for a future transition to Django models)
• got rid of all derivable redundant data in the index files
• Much faster performance when passing over old links by avoiding excessive index writes
• Entirely new UI for the Index Details page: