Implement "transition-duration" for individual steps.

Closes gh-6.

gh-pages/demo/index.html

@@ -162,8 +162,11 @@
         
         It will not be rotated or scaled.
         
+        Also, you can optionally specify `data-transition-duration="300"` for individual steps.
+        It defaults to the values specified in the `#impress` element.
+        
     -->
-    <div id="bored" class="step slide" data-x="-1000" data-y="-1500">
+    <div id="bored" class="step slide" data-x="-1000" data-y="-1500" data-transition-duration="300">
         <q>Aren't you just <b>bored</b> with all those slides-based presentations?</q>
     </div>
 
@@ -182,11 +185,11 @@
         Using classic `id`-based links like `#step-2` makes these links usable also in fallback mode.
         
     -->
-    <div class="step slide" data-x="0" data-y="-1500">
+    <div class="step slide" data-x="0" data-y="-1500" data-transition-duration="300">
         <q>Don't you think that presentations given <strong>in modern browsers</strong> shouldn't <strong>copy the limits</strong> of 'classic' slide decks?</q>
     </div>
 
-    <div class="step slide" data-x="1000" data-y="-1500">
+    <div class="step slide" data-x="1000" data-y="-1500" data-transition-duration="300">
         <q>Would you like to <strong>impress your audience</strong> with <strong>stunning visualization</strong> of your talk?</q>
     </div>
 

src/js/core.js

@@ -57,7 +57,7 @@ var css = function( element, props ) {
 };
 
 // Takes a value given as `numeric` parameter and tries to turn it into a number. If it is not
-// possible it returns 0 (or other value given as `fallback`).
+//possible it returns 0 (or other value given as `fallback`).
 var toNumber = function( numeric, fallback ) {
 	return isNaN( numeric ) ? ( fallback || 0 ) : Number( numeric );
 };
@@ -407,7 +407,7 @@ var impress = function( argument ) {
 	// Used to reset timeout for `impress:stepenter` event.
 	var stepEnterTimeout = null;
 
-	// API function that moves to step according to the `argument` parameter (by index, id
+	// API function that moves to step according to the `argument` parameter (by step index, id
 	// or element), with a transition `duration` optionally given as second parameter.
 	var goto = function( argument, duration ) {
 		var element = getStep( argument );
@@ -462,7 +462,14 @@ var impress = function( argument ) {
 		// zooming out we start with scaling down and move and rotation are delayed.
 		var zoomin = target.scale >= currentState.scale;
 
-		duration = toNumber( duration, config.transitionDuration );
+		// If a duration was specified, use that, otherwise use the step data attribute.
+		var stepData = element.dataset;
+		if ( arguments.length > 1 ) {
+			duration = toNumber( duration, config.transitionDuration );
+		} else {
+			duration = toNumber( stepData.transitionDuration, config.transitionDuration );
+		}
+
 		var delay = duration / 2;
 
 		// If the same step is re-selected, force computing window scaling, because it is likely