Make created GPX file valid

Validated with SAXCount from the xerces-c package:

    $ SAXCount -v=always -n -s -f notes.gpx

Error messages before this change:

    Error at file /home/markus/note.gpx, line 2, char 84
      Message: no declaration found for element 'gpx'

    Error at file /home/markus/note.gpx, line 2, char 84
      Message: attribute 'version' is not declared for element 'gpx'

    Error at file /home/markus/note.gpx, line 2, char 84
      Message: attribute 'creator' is not declared for element 'gpx'

    Error at file /home/markus/note.gpx, line 2, char 84
      Message: attribute 'xmlns' is not declared for element 'gpx'

    Error at file /home/markus/note.gpx, line 3, char 41
      Message: no declaration found for element 'wpt'

    Error at file /home/markus/note.gpx, line 3, char 41
      Message: attribute 'lat' is not declared for element 'wpt'

    Error at file /home/markus/note.gpx, line 3, char 41
      Message: attribute 'lon' is not declared for element 'wpt'

    Error at file /home/markus/note.gpx, line 4, char 11
      Message: no declaration found for element 'name'

    Error at file /home/markus/note.gpx, line 5, char 10
      Message: no declaration found for element 'cmt'

Author: marcows

osmnotes.pl

@@ -87,6 +87,8 @@
 $gpxroot->addChild($final_gpx->createAttribute(version => '1.1'));
 $gpxroot->addChild($final_gpx->createAttribute(creator => 'osmnotes.pl'));
 $gpxroot->addChild($final_gpx->createAttribute(xmlns => 'http://www.topografix.com/GPX/1/1'));
+$gpxroot->addChild($final_gpx->createAttribute('xmlns:xsi' => 'http://www.w3.org/2001/XMLSchema-instance'));
+$gpxroot->addChild($final_gpx->createAttribute('xsi:schemaLocation' => 'http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd'));
 
 sub parse_note {
 	my ($note) = @_;