Add spec for nested iteration (issue #79)

spec/_files/nested_iterating.js

@@ -0,0 +1,8 @@
+var nested_iterating = {
+  inner: [{
+    foo: 'foo',
+    inner: [{
+      bar: 'bar'
+    }]
+  }]
+};

spec/_files/nested_iterating.mustache

@@ -0,0 +1 @@
+{{#inner}}{{foo}}{{#inner}}{{bar}}{{/inner}}{{/inner}}

spec/_files/nested_iterating.txt

@@ -0,0 +1 @@
+foobar