Improve the hyper-schema abstract

Use language more in line with recent changes and recently
introduced concepts.  Add a little more detail about the
general capabilities.  This is all roughly inspired by reading
the guidelineson abstracts in RFC 7322 section 4.3

Author: handrews

jsonschema-hyperschema.xml

@@ -57,10 +57,13 @@
 
         <abstract>
             <t>
-                JSON Schema is a JSON based format for describing JSON data using various
-                vocabularies.  This document specifies a vocabulary
-                for annotating JSON documents with hyperlinks and instructions for processing and
-                manipulating remote JSON resources through hypermedia environments such as HTTP.
+                JSON Schema is a JSON-based format for describing JSON data using various
+                vocabularies.  This document specifies a vocabulary for annotating JSON
+                documents with hyperlinks.  These hyperlinks include attributes describing
+                how to manipulate and interact with remote resources through hypermedia
+                environments such as HTTP, as well as determining whether the link is usable
+                based on the instance value.  The hyperlink serialization format described in
+                this document is also usable independent of JSON Schema.
             </t>
         </abstract>
         <note title="Note to Readers">