Incorrect reader/writer initialization in examples and description

[AndreasKorn]

The reader/writer initialization code and description in the examples is not correct and leads to bad side effects and unexpected results (You need to instantiate the classes in the init context).

Since the "init" context is executed multiple times during the script execution the readers and writers are also instantiated multiple times.
Especially for the reader (consumer) this is really bad as you will have multiple consumers in the group if you do not use a unique group id, meaning you will not get all messages.
And even if you use a unique group id multiple consumers mean more active reader meaning more load.

The writers and readers should be instantiated and cleaned up in the default function.