Ongoing review of PR #2

[michaeljklein]

PR #2 (Support Parsing JSON) is being merged, but since it's such a large zero-to-one change, it'll need ongoing review.

Housekeeping:

• Do module boundaries make sense?
• API documentation?
• Clippy setup?

Review topics:

• Idiomatic rust
• Rust architecture
• Language design: parsing, features, semantics, types
• Roadmap and project goals