Add event submission and change fetch to use URL

In the description for events I have added a new operation to submit new events,
this submission returns an array with one member 'url'. The url member points to
the newly created event.

In addition I have changed the `fetch` operation to use a URL as parameter; this
will allow the user to fetch a given event in HATEOAS style.
Add support for Talks

In this commit I have added the option to retrieve a series of talks for an
event's talks_url, one specific talk by its own URL and to submit a new talk
on the talks collection for an event (identified by the talks_url).
Add examples for various actions.

In order to help people to use this client code I have included
a series of examples. These examples are also the pieces of code
I use for manual testing so that is a big win.
Simplify base example

Because we make elaborate examples in the examples folder
but I still want to keep knowing how to use the client as
simple as can be I have simplified the example and referred
to the examples folder.