Improve config parser structure, error handling and style

[literally-user]

Improved config parser structure, error handling and style

• Split code into functions for better organization
• Added error handling for file reading
• Replaced os.path with pathlib for cleaner path handling
• Improved regex to handle spaces better
• Used return codes instead of multiple sys.exit calls
• Added help messages for CLI arguments
• Output errors to stderr
• Cleaned up formatting for readability

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