docs: add comprehensive language documentation
Documentation structure inspired by Rust Book, Elm Guide, and others:
Guide (10 chapters):
- Introduction and setup
- Basic types (Int, String, Bool, List, Option, Result)
- Functions (closures, higher-order, composition)
- Data types (ADTs, pattern matching, records)
- Effects (the core innovation)
- Handlers (patterns and techniques)
- Modules (imports, exports, organization)
- Error handling (Fail, Option, Result)
- Standard library reference
- Advanced topics (traits, generics, optimization)
Reference:
- Complete syntax reference
Tutorials:
- Calculator (parsing, evaluation, REPL)
- Dependency injection (testing with effects)
- Project ideas (16 projects by difficulty)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>