Added syntax-plugin to create in-page site export downloader

This will actually print a list of pages, ordered by a META key (needs
meta plugin). These pages will then be put into a <toc> element and
merged into one big document. In addition: headers of these will be
merged. I think that you will be able to specify more options later.
The syntax-key has changed.
Moved siteexportmanager.php to exe to satisfy default apache config for DW