feat(markdown): add content source selection for markdown generation

Adds a new content_source parameter to MarkdownGenerationStrategy that allows
selecting which HTML content to use for markdown generation:
- cleaned_html (default): uses post-processed HTML
- raw_html: uses original webpage HTML
- fit_html: uses preprocessed HTML for schema extraction

Changes include:
- Added content_source parameter to MarkdownGenerationStrategy
- Updated AsyncWebCrawler to handle HTML source selection
- Added examples and tests for the new feature
- Updated documentation with new parameter details

BREAKING CHANGE: Renamed cleaned_html parameter to input_html in generate_markdown()
method signature to better reflect its generalized purpose

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to Crawl4AI will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+### [Added] 2025-04-17
+- Added content source selection feature for markdown generation
+  - New `content_source` parameter allows choosing between `cleaned_html`, `raw_html`, and `fit_html`
+  - Provides flexibility in how HTML content is processed before markdown conversion
+  - Added examples and documentation for the new feature
+  - Includes backward compatibility with default `cleaned_html` behavior
+  
 ## Version 0.5.0.post5 (2025-03-14)
 
 ### Added