Add spec for context lookup (issue #122)

spec/_files/context_lookup.js

@@ -0,0 +1,8 @@
+var context_lookup = {
+  "outer": {
+    "id": 1,
+    "second": {
+      "nothing": 2
+    }
+  }
+};

spec/_files/context_lookup.mustache

@@ -0,0 +1 @@
+{{#outer}}{{#second}}{{id}}{{/second}}{{/outer}}

spec/_files/context_lookup.txt

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