feat: add configuration loader for .env and JSON files

- Add ConfigLoader class for loading RateLimitConfig and GlobalConfig
- Support .env files with FASTAPI_TRAFFIC_* prefixed variables
- Support JSON configuration files with type validation
- Add convenience functions: load_rate_limit_config, load_global_config
- Add load_rate_limit_config_from_env, load_global_config_from_env
- Support custom environment variable prefixes
- Add comprehensive error handling with ConfigurationError
- Add 47 tests for configuration loading
- Add example 11_config_loader.py with 9 usage patterns
- Update examples/README.md with config loader documentation
- Update CHANGELOG.md with new feature
- Fix typo in limiter.py (errant 'fi' on line 4)

examples/README.md

@@ -5,13 +5,17 @@ This directory contains comprehensive examples demonstrating how to use the `fas
 ## Basic Examples
 
 ### 01_quickstart.py
+
 Minimal setup to get rate limiting working. Start here if you're new to the library.
+
 - Basic backend and limiter setup
 - Exception handler for rate limit errors
 - Simple decorator usage
 
 ### 02_algorithms.py
+
 Demonstrates all available rate limiting algorithms:
+
 - **Fixed Window** - Simple, resets at fixed intervals
 - **Sliding Window** - Most precise, stores timestamps
 - **Sliding Window Counter** - Balance of precision and efficiency (default)
@@ -19,13 +23,17 @@ Demonstrates all available rate limiting algorithms:
 - **Leaky Bucket** - Smooths out traffic
 
 ### 03_backends.py
+
 Shows different storage backends:
+
 - **MemoryBackend** - Fast, ephemeral (default)
 - **SQLiteBackend** - Persistent, single-instance
 - **RedisBackend** - Distributed, multi-instance
 
 ### 04_key_extractors.py
+
 Custom key extractors for different rate limiting strategies:
+
 - Rate limit by IP address (default)
 - Rate limit by API key
 - Rate limit by user ID
@@ -34,7 +42,9 @@ Custom key extractors for different rate limiting strategies:
 - Composite keys (user + action)
 
 ### 05_middleware.py
+
 Middleware-based rate limiting for global protection:
+
 - Basic middleware setup
 - Custom configuration options
 - Path and IP exemptions
@@ -43,35 +53,45 @@ Middleware-based rate limiting for global protection:
 ## Advanced Examples
 
 ### 06_dependency_injection.py
+
 Using FastAPI's dependency injection system:
+
 - Basic rate limit dependency
 - Tier-based rate limiting
 - Combining multiple rate limits
 - Conditional exemptions
 
 ### 07_redis_distributed.py
+
 Redis backend for distributed deployments:
+
 - Multi-instance rate limiting
 - Shared counters across nodes
 - Health checks and statistics
 - Fallback to memory backend
 
 ### 08_tiered_api.py
+
 Production-ready tiered API example:
+
 - Free, Starter, Pro, Enterprise tiers
 - Different limits per tier
 - Feature gating based on tier
 - API key validation
 
 ### 09_custom_responses.py
+
 Customizing rate limit responses:
+
 - Custom JSON error responses
 - Logging/monitoring callbacks
 - Different response formats (JSON, HTML, plain text)
 - Rate limit headers
 
 ### 10_advanced_patterns.py
+
 Real-world patterns and use cases:
+
 - **Cost-based limiting** - Different operations cost different amounts
 - **Priority exemptions** - Premium users exempt from limits
 - **Resource-based limiting** - Limit by resource ID + user
@@ -81,6 +101,23 @@ Real-world patterns and use cases:
 - **Time-of-day limits** - Peak vs off-peak hours
 - **Cascading limits** - Per-second, per-minute, per-hour
 
+### 11_config_loader.py
+
+Loading configuration from external files:
+
+- **Environment variables** - Load from `FASTAPI_TRAFFIC_*` env vars
+- **.env files** - Load from dotenv files for local development
+- **JSON files** - Load from JSON for structured configuration
+- **Custom prefixes** - Use custom env var prefixes
+- **Validation** - Automatic type validation and error handling
+- **Environment-based config** - Different configs for dev/staging/prod
+
+Run with `--demo` flag to see all configuration examples:
+
+```bash
+python examples/11_config_loader.py --demo
+```
+
 ## Running Examples
 
 Each example is a standalone FastAPI application. Run with: