[WIP] Fix issue #14 to ensure mdbook-embedify compatibility with mdbook V0.5

[Copilot]

• Update Cargo.toml to use mdbook 0.5.x and mdbook-preprocessor crate
• Update imports in main.rs to use mdbook-preprocessor functions
• Update imports in embed.rs if needed
• Update Preprocessor::supports_renderer to return Result
• Test compilation with mdbook 0.5
• Run existing tests to ensure compatibility
• Update documentation if needed

Original prompt

try to fix issue #14, make mdbook-embedify compitable with mdbook V0.5

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