Add support for LLVM's SVN history
Add support for LLVM's SVN history

This is useful when developing LLVM in the wasm-e2e clone of LLVM. The the URL in the comment for Official Reference (TM).

I also added some documentation, and bit more error handling (the script should die on unknown parameters).

WebAssembly/wasm-e2e,binji/wasm-e2e,binji/wasm-e2e,WebAssembly/wasm-e2e,binji/wasm-e2e,WebAssembly/wasm-e2e,WebAssembly/wasm-e2e,WebAssembly/wasm-e2e,binji/wasm-e2e