Add comprehensive test suite for basic markdown syntax features:
- basic-headings.md: All heading levels and setext syntax
- basic-paragraphs-line-breaks.md: Paragraph separation and line breaks
- basic-emphasis.md: Bold and italic formatting
- basic-blockquotes.md: Blockquotes with nested content
- basic-lists.md: Ordered and unordered lists with nesting
- basic-code.md: Inline code and code blocks
- basic-horizontal-rules.md: Horizontal rule variants
- basic-links-and-images.md: Links and images with various syntax
- basic-escaping.md: Character escaping
- basic-index.md: Index of all test files
All files follow the Markdown Guide's Basic Syntax specification.
