feat(cli): add command line interface with comprehensive features

Implements a full-featured CLI for Crawl4AI with the following capabilities:
- Basic and advanced web crawling
- Configuration management via YAML/JSON files
- Multiple extraction strategies (CSS, XPath, LLM)
- Content filtering and optimization
- Interactive Q&A capabilities
- Various output formats
- Comprehensive documentation and examples

Also includes:
- Home directory setup for configuration and cache
- Environment variable support for API tokens
- Test suite for CLI functionality

crawl4ai/extraction_strategy.py

@@ -533,11 +533,15 @@ class LLMExtractionStrategy(ExtractionStrategy):
         """
         super().__init__(**kwargs)
         self.provider = provider
-        self.api_token = (
-            api_token
-            or PROVIDER_MODELS.get(provider, "no-token")
-            or os.getenv("OPENAI_API_KEY")
-        )
+        if api_token and not api_token.startswith("env:"):
+            self.api_token = api_token
+        elif api_token and api_token.startswith("env:"):
+            self.api_token = os.getenv(api_token[4:])
+        else:
+            self.api_token = (
+                PROVIDER_MODELS.get(provider, "no-token")
+                or os.getenv("OPENAI_API_KEY")
+            )
         self.instruction = instruction
         self.extract_type = extraction_type
         self.schema = schema