v0.3.0

✨ Cell Formatting - 14 predefined styles: bold, italic, highlights, borders, number formats!
🎨 Easy Styling API - write_header_bold(), write_row_styled(), write_row_with_style()
💰 Number Formats - Currency, percentage, decimal, integer formats
🎨 Text Styles - Bold, italic, yellow/green/red highlights
📅 Date Formats - MM/DD/YYYY and timestamp formats