Fix bug on data attributes for first vertical slide.

The first slide of a vertical stack see some data attributes ignored.

Mainly the data-transition one.

Repeat all data-attributes on the wrapping section element.

Ignore any other attributes (like 'id="xxx"'), in order to not
mess with internal links (by repeating twice an id).

plugin/markdown/markdown.js

@@ -178,12 +178,25 @@
 		for( var i = 0, len = sectionStack.length; i < len; i++ ) {
 			// vertical
 			if( sectionStack[i] instanceof Array ) {
-				markdownSections += '<section '+ options.attributes +'>';
+				// The 'data-xxx' attributes of the first child must be set on the wrapping parent section to be effective
+				// Mainly for data-transition (otherwise, it is ignored for the first vertical slide)
+				firstChild = sectionStack[i][0];
+				matchAttributes = slideAttributesSeparatorRegex.exec(firstChild);
+				slideAttributes = matchAttributes ? matchAttributes[1] : "";
+				if( slideAttributes != "") {
+					// console.log('all attr=' + slideAttributes );
+					// http://stackoverflow.com/questions/18025762/javascript-regex-replace-all-word-characters-except-word-characters-between-ch
+					// Keep only data-attributes for the parent slide section.
+					dataAttributes = slideAttributes.replace(/(data-\S+=\"[^\"]+?\")|\w|[\"=]/g, function(a, b) { return b || ''; });
+					// console.log('new attr=' + dataAttributes );
+					markdownSections += '<section '+ options.attributes + ' ' + dataAttributes + '>';
+				}
 
 				sectionStack[i].forEach( function( child ) {
 					matchAttributes = slideAttributesSeparatorRegex.exec(child);
 					slideAttributes = matchAttributes ? matchAttributes[1] : "";
 					child = matchAttributes ? child.replace(slideAttributesSeparatorRegex,"") : child
+					// console.log('slide attributes ' + options.slideAttributesSeparator + ' => ' + slideAttributes)
 					markdownSections += '<section ' + slideAttributes + ' data-markdown>' +  createMarkdownSlide( child, options ) + '</section>';
 				} );