Library restructure (#104)

* Move wasmer-runtime to wasmer-runtime-core

* Add the runtime library

* Fix issue with macros using wasmer_runtime, fmt

* Make default compiler dependency optional

* Add instantiate and validate functions

lib/runtime-core/examples/simple/main.rs

@@ -0,0 +1,43 @@
+use wabt::wat2wasm;
+use wasmer_clif_backend::CraneliftCompiler;
+use wasmer_runtime_core::{error::Result, prelude::*};
+
+static EXAMPLE_WASM: &'static [u8] = include_bytes!("simple.wasm");
+
+fn main() -> Result<()> {
+    let wasm_binary = wat2wasm(IMPORT_MODULE.as_bytes()).expect("WAST not valid or malformed");
+    let inner_module = wasmer_runtime_core::compile_with(&wasm_binary, &CraneliftCompiler::new())?;
+
+    let import_object = imports! {
+        "env" => {
+            "print_i32" => print_num<[i32] -> [i32]>,
+        },
+    };
+
+    let inner_instance = inner_module.instantiate(import_object)?;
+
+    let outer_imports = imports! {
+        "env" => inner_instance,
+    };
+
+    let outer_module = wasmer_runtime_core::compile_with(EXAMPLE_WASM, &CraneliftCompiler::new())?;
+    let mut outer_instance = outer_module.instantiate(outer_imports)?;
+    let ret = outer_instance.call("main", &[Value::I32(42)])?;
+    println!("ret: {:?}", ret);
+
+    Ok(())
+}
+
+extern "C" fn print_num(n: i32, _vmctx: &mut vm::Ctx) -> i32 {
+    println!("print_num({})", n);
+    n + 1
+}
+
+static IMPORT_MODULE: &str = r#"
+(module
+  (type $t0 (func (param i32) (result i32)))
+  (import "env" "print_i32" (func $print_i32 (type $t0)))
+  (func $print_num (export "print_num") (type $t0) (param $p0 i32) (result i32)
+    get_local $p0
+    call $print_i32))
+"#;