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/src/import.rs

@@ -0,0 +1,60 @@
+use crate::export::Export;
+use hashbrown::{hash_map::Entry, HashMap};
+
+pub trait LikeNamespace {
+    fn get_export(&mut self, name: &str) -> Option<Export>;
+}
+
+pub struct ImportObject {
+    map: HashMap<String, Box<dyn LikeNamespace>>,
+}
+
+impl ImportObject {
+    pub fn new() -> Self {
+        Self {
+            map: HashMap::new(),
+        }
+    }
+
+    pub fn register<S, N>(&mut self, name: S, namespace: N) -> Option<Box<dyn LikeNamespace>>
+    where
+        S: Into<String>,
+        N: LikeNamespace + 'static,
+    {
+        match self.map.entry(name.into()) {
+            Entry::Vacant(empty) => {
+                empty.insert(Box::new(namespace));
+                None
+            }
+            Entry::Occupied(mut occupied) => Some(occupied.insert(Box::new(namespace))),
+        }
+    }
+
+    pub fn get_namespace(&mut self, namespace: &str) -> Option<&mut (dyn LikeNamespace + 'static)> {
+        self.map
+            .get_mut(namespace)
+            .map(|namespace| &mut **namespace)
+    }
+}
+
+pub struct Namespace {
+    map: HashMap<String, Export>,
+}
+
+impl Namespace {
+    pub fn new() -> Self {
+        Self {
+            map: HashMap::new(),
+        }
+    }
+
+    pub fn insert(&mut self, name: impl Into<String>, export: Export) -> Option<Export> {
+        self.map.insert(name.into(), export)
+    }
+}
+
+impl LikeNamespace for Namespace {
+    fn get_export(&mut self, name: &str) -> Option<Export> {
+        self.map.get(name).cloned()
+    }
+}