See http://stackoverflow.com/a/3568906/818821

Squashed commit of the following:

commit b5d5dd8
Author: Timothy Kist <zboarda@gmail.com>
Date:   Wed Oct 12 14:51:15 2016 +0100

    Improve valid observable tests

commit 93de1cc
Author: Timothy Kist <zboarda@gmail.com>
Date:   Wed Oct 12 14:26:32 2016 +0100

    Fix default connectivity check

commit 730b575
Author: Timothy Kist <zboarda@gmail.com>
Date:   Wed Oct 12 14:25:31 2016 +0100

    Add tests for valid observables

commit e93367d
Author: Timothy Kist <zboarda@gmail.com>
Date:   Wed Oct 12 13:52:07 2016 +0100

    Add tests for observing internet with initial interval

commit 3c6b52a
Author: Timothy Kist <zboarda@gmail.com>
Date:   Tue Oct 11 12:40:14 2016 +0100

    Add documentation for checking internet connectivity immediately or specifying inital interval

commit c18861e
Author: Timothy Kist <zboarda@gmail.com>
Date:   Tue Oct 11 12:38:16 2016 +0100

    Remove API documentation noise by removing redundant `final` keyword

commit 22fd32f
Author: Timothy Kist <zboarda@gmail.com>
Date:   Tue Oct 11 12:30:36 2016 +0100

    Correct exception message

commit fed5904
Author: Timothy Kist <zboarda@gmail.com>
Date:   Tue Oct 11 12:29:26 2016 +0100

    Add default intial ping interval

commit 91671ec
Author: Tim Kist <timkist@imagitech.co.uk>
Date:   Fri Oct 7 16:42:53 2016 +0100

    Add check internet connectivity immediately