Added links to wiki pages,

where they already exist. The bullet lists that have no links should also,
over time, get links that expand on their claims, but currently, these
pages don't exist.
Copied write examples to Visitor demo,

in order to use the write examples in the documentation, instead of the
current examples that use AtomEventObserver<object>, because at a glance,
it looks better that the generic type argument is bing used properly.
Updated the XML doc examples to use new examples

with stronger generic type argument.