add ping and ping factory
improve readability of Foaf_Person
add aair:activityContext the 4th and optinal part of an aair:Activity to lib
add more objects and verbs
add classes of new objects and verbs
change feed child nodes
change static invocation of DOMDocument::loadXML
little change to previous commit
add default cases when reading a feed with unknown objects or verbs
import some more attributes of feed and activity when reading an incoming feed
import some more attributes of feed and activity when reading an incoming feed
import some more attributes of feed and activity when reading an incoming feed
change stacic call DOMDocument::load()
fix newFromUrl() method to follow redirects
add links to DSSN_Activity_Feed in factory