Fix GitHub newlines issue #83 using markdown files approach

[bhouston]

Fix for GitHub newlines issue #83 using markdown files approach

This PR implements an alternative approach to fix issue #83 where newlines and formatting in GitHub issues, PRs, and comments weren't being preserved correctly.

Changes

1. Updated the GitHub mode instructions in the system prompt to use temporary markdown files:

   • Create a temporary markdown file with the content
   • Use the file with GitHub CLI commands (e.g., gh issue create --body-file temp.md)
   • Clean up the temporary file when done

2. Added documentation in README.md about this approach with examples

3. Created a test file showing how this approach works

Benefits

• More robust than trying to escape newlines in inline text
• Preserves formatting, newlines, and special characters correctly
• Works consistently across different platforms (Windows, Linux, macOS)
• Follows standard GitHub CLI practices for handling complex content

Closes #83