Add clif-backend crate and runtime example

lib/runtime/examples/simple/main.rs

@@ -0,0 +1,13 @@
+use wasmer_runtime as runtime;
+use wasmer_clif_backend::CraneliftCompiler;
+
+static EXAMPLE_WASM: &'static [u8] = include_bytes!("simple.wasm");
+
+fn main() {
+    let compiler = CraneliftCompiler::new();
+    let module = runtime::compile(EXAMPLE_WASM, &compiler).unwrap();
+    let imports = runtime::Imports::new();
+    let mut instance = module.instantiate(&imports).unwrap();
+    let ret = instance.call("main", &[runtime::types::Value::I32(42)]);
+    println!("ret: {:?}", ret);
+}