Add context and context_mut methods to Instance

lib/runtime-core/src/instance.rs

@@ -159,10 +159,29 @@ impl Instance {
         self.call_with_index(func_index, args)
     }
 
+    /// Returns a immutable reference to the
+    /// [`Ctx`] used by this Instance.
+    ///
+    /// [`Ctx`]: struct.Ctx.html
+    pub fn context(&self) -> &vm::Ctx {
+        &self.inner.vmctx
+    }
+
+    /// Returns a mutable reference to the
+    /// [`Ctx`] used by this Instance.
+    ///
+    /// [`Ctx`]: struct.Ctx.html
+    pub fn context_mut(&mut self) -> &mut vm::Ctx {
+        &mut self.inner.vmctx
+    }
+
+    /// Returns a iterator over all of the items
+    /// exported from this instance.
     pub fn exports(&mut self) -> ExportIter {
         ExportIter::new(&self.module, &mut self.inner)
     }
 
+    /// The module used to instantiate this Instance.
     pub fn module(&self) -> Module {
         Module::new(Rc::clone(&self.module))
     }