corrected errors; added egs of events & relations

I added the actual Arabic description of Edessa.  I found 2]3 values of
@source attributes which omitted the '#' character before the xml:id of
the <bibl>.  I added two events to Edessa <place xml:id="SRP-id-78">.  I
encoded the Tigris river and Chalcedon in order to show other examples
of events, BUT FOR THOSE EVENTS I DO NOT HAVE SOURCES, SO THEY SHOULD
NOT BE PUBLISHED.  I added two relations using <relation> elements, one
between places and one between a place and a person.