support scraping start-/enddate from html tag with property "datetime"

This may be used in html5 <time> tag (which we don't explicite support yet for date in content scraping).

source/net/yacy/document/parser/html/ContentScraper.java

@@ -389,16 +389,17 @@ public class ContentScraper extends AbstractScraper implements Scraper {
         // itemprop
         String itemprop = tag.opts.getProperty("itemprop");
         if (itemprop != null) {
-            String content = tag.opts.getProperty("content");
-            if (content != null) {
+            String propval = tag.opts.getProperty("content");
+            if (propval == null) propval = tag.opts.getProperty("datetime"); // html5 example: <time itemprop="startDate" datetime="2016-01-26">today</time> while each prop is optional
+            if (propval != null) {
                 if ("startDate".equals(itemprop)) try {
                     // parse ISO 8601 date
-                    Date startDate = ISO8601Formatter.FORMATTER.parse(content, this.timezoneOffset).getTime();
+                    Date startDate = ISO8601Formatter.FORMATTER.parse(propval, this.timezoneOffset).getTime();
                     this.startDates.add(startDate);
                 } catch (ParseException e) {}
                 if ("endDate".equals(itemprop)) try {
                     // parse ISO 8601 date
-                    Date endDate = ISO8601Formatter.FORMATTER.parse(content, this.timezoneOffset).getTime();
+                    Date endDate = ISO8601Formatter.FORMATTER.parse(propval, this.timezoneOffset).getTime();
                     this.endDates.add(endDate);
                 } catch (ParseException e) {}
             }