added test case for string as a context

spec/_files/string_as_context.js

@@ -0,0 +1,4 @@
+var string_as_context = {
+    a_string: 'aa',
+    a_list: ['a','b','c']
+};

spec/_files/string_as_context.mustache

@@ -0,0 +1,5 @@
+<ul>
+{{#a_list}}
+    <li><a href="#{{a_string}}/{{.}}">{{.}}</a></li>
+{{/a_list}}
+</ul>

spec/_files/string_as_context.txt

@@ -0,0 +1,5 @@
+<ul>
+    <li><a href="#aa/a">a</a></li>
+    <li><a href="#aa/b">b</a></li>
+    <li><a href="#aa/c">c</a></li>
+</ul>