Configure as library, add demo

demo/.gitignore

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+/target

demo/Cargo.toml

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+[package]
+name = "renrs-demo"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+renrs = { path = ".." }

demo/src/main.rs

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+use renrs;
+
+fn main() {
+    renrs::hello();
+}