Tutorial for talloc and tevent libraries

Many network services use the concept of event libraries to achieve better
performance by avoiding blocking I/O calls and using the concept of callbacks
instead. One of the event libraries in use is tevent, used by the Samba project
or the SSSD daemon.

Unfortunately, there is no documentation for tevent, which raises the bar for
new contributors significantly. The goal of this bachelor thesis is to provide
developer-oriented documentation for tevent, including tutorial and examples.

The thesis will include:

  - an introduction and tutorial to talloc, the underlying memory allocator that
    tevent (and Samba and SSSD themselves) use. There is only incomplete API
reference to talloc, no tutorial either.
  - an overview of the concept of event libraries, how they work under the hood
    (/dev/poll, select(), epoll(), etc.) a developer tutorial that gradually
explains the concepts of event libraries and tevent in particular. The tutorial
should include examples, ranging from simple library initialization to complex
nested asynchronous events.
  - a comparison of tevent and other event libraries (libevent for example).

The tutorial with examples should be discussed with the tevent upstream.