* Adds a new tab link in xmlsitemap's administration page
* Removes drush and purge experimental functionalities from 7.x-1.x
* Adds the xhc_cron submodule to set xmlsitemap's http cache generation cron tasks with Elysia cron
* API change: xhc_generate($smid, $cron) instead of xhc_generate($lang, $drush)
