Squashed commit of the following:

commit 0e89627e5d6c39af9a7f75ca20c693dc757454cf
Author: Kaspar Schleiser <kaspar@schleiser.de>
Date:   Fri Apr 4 08:14:35 2014 +0200

    native: auto exit: use EXIT_SUCCESS, add safty for exit condition

commit c4e21338f1c5841ff74b00860fd982419704f6c2
Author: Kaspar Schleiser <kaspar@schleiser.de>
Date:   Fri Apr 4 08:14:12 2014 +0200

    native: README remove trailing newline

commit 2060288c14e9fc6716edfd9ac6426c35eec80448
Author: Kaspar Schleiser <kaspar@schleiser.de>
Date:   Thu Apr 3 17:41:19 2014 +0200

    native: document NATIVE_AUTO_EXIT

commit cf46daf0e072b656ef9bba4e47b0fdaaf958460a
Author: Kaspar Schleiser <kaspar@schleiser.de>
Date:   Thu Apr 3 17:39:51 2014 +0200

    native: make auto exit optional

commit 5f83d670bc49240bd2edb4b5d686558b793ff4b1
Author: Kaspar Schleiser <kaspar@schleiser.de>
Date:   Sat Jan 25 15:33:03 2014 +0100

    native: exit() after last thread has ended