Add example showing use of compact IRIs in contexts

Added an example which shows how compact IRIs can be used in a context.

This addresses #74. I'll leave the issue open as long as the API spec hasn't been updated.

Author: lanthaler

spec/latest/json-ld-syntax/index.html

@@ -1376,6 +1376,26 @@ <h2>Compact IRIs</h2>
     are referred to using prefixes. Those prefixes are then used as type and
     property values using the compact IRI <code>prefix:suffix</code> notation.
   </p>
+  <p>It's also possible to use compact IRIs within the context as shown in the
+    following example:<p>
+  <pre class="example" data-transform="updateExample">
+<!--
+{
+  "@context":
+  {
+    "xsd": "http://www.w3.org/2001/XMLSchema#",
+    "foaf": "http://xmlns.com/foaf/0.1/",
+    ****"foaf:homepage"****: { "@type": "@id" },
+    "picture": { "@id": ****"foaf:depiction"****, "@type": "@id" }
+  },
+  "@subject": "http://me.markus-lanthaler.com/",
+  "@type": "foaf:Person",
+  "foaf:name": "Markus Lanthaler",
+  "foaf:homepage": "http://www.markus-lanthaler.com/",
+  "picture": "http://twitter.com/account/profile_image/markuslanthaler"
+}
+-->
+  </pre>
   <p>
     <tref title="compact_iri">Compact IRIs</tref>, also known as CURIEs, are defined more formally in RDFa Core 1.1,
     <cite><a href="http://www.w3.org/TR/rdfa-core/#s_curies">Section 6