Minimal Rust C FFI example

Keypoints

• Add build = "src/build.rs" in Cargo.toml (otherwise cargo sometimes fails to pick it up and I don't know why)
• #[link(name = "hello", kind = "dylib")] (or another kind; in this case a dylib)
• cargo:rustc-link-search flag in build.rs file
• Set environment variables correctly (Linux: LD_LIBRARY_PATH, Mac: DYLD_LIBRARY_PATH)

build_and_run bash script sets enviroment variables for you; you may want to take a look at it.