Add autoplay URL parameter trigger. (#764)

Resolves #720

src/lib/util.js

@@ -49,6 +49,17 @@
             return byId( window.location.hash.replace( /^#\/?/, "" ) );
         };
 
+        // `getUrlParamValue` return a given URL parameter value if it exists
+        // `undefined` if it doesn't exist
+        var getUrlParamValue = function( parameter ) {
+            var chunk = window.location.search.split( parameter + "=" )[ 1 ];
+            var value = chunk && chunk.split( "&" )[ 0 ];
+
+            if ( value !== "" ) {
+                return value;
+            }
+        };
+
         // Throttling function calls, by Remy Sharp
         // http://remysharp.com/2010/07/21/throttling-function-calls/
         var throttle = function( fn, delay ) {
@@ -85,7 +96,8 @@
             getElementFromHash: getElementFromHash,
             throttle: throttle,
             toNumber: toNumber,
-            triggerEvent: triggerEvent
+            triggerEvent: triggerEvent,
+            getUrlParamValue: getUrlParamValue
         };
         roots[ rootId ] = lib;
         return lib;