Add an example of console.log

Also clean up some other exampels

examples/console_log/src/lib.rs

@@ -0,0 +1,18 @@
+#![feature(proc_macro)]
+
+extern crate wasm_bindgen;
+
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+extern {
+    type console;
+
+    #[wasm_bindgen(static = console)]
+    fn log(s: &str);
+}
+
+#[wasm_bindgen]
+pub fn run() {
+    console::log("Hello from Rust!");
+}