Changing echo/print in examples to use (var_)dump

[linaori]

I think the code should be looked through and see if usages of echo and print can be limited. I think the best replacement could be a reference to dump() to output data, but a var_dump() could be sufficient too, depending on whether it's framework or a component documentation. An example of using echo can be found on /components/event_dispatcher/introduction.html#event-name-introspection

[wouterj]

Actually, why don't we remove the echo and just use // ... do something with the eventname in $name?

[linaori]

It's an option, but might not apply to all output-using examples. For this page it might be nicer to indeed use a comment.