Add started_at timestamp

Closes #97

LGTM given by: @jornvandebeek

Squashed commit of the following:

commit 564b29b3a30399549517ced5b6da8e23eca462be
Author: Marten Veldthuis <marten@veldthuis.com>
Date:   Mon Sep 29 15:49:17 2014 +0200

    bump version

commit 23fb18c2796d640e0874ddc3b9c60b0f4831fc01
Author: Marten Veldthuis <marten@veldthuis.com>
Date:   Mon Sep 29 15:46:35 2014 +0200

    Undo more spaces

commit 47d599ebdc10e7227368f1ce5de02c1cfbe05e0b
Author: Marten Veldthuis <marten@veldthuis.com>
Date:   Mon Sep 29 15:45:58 2014 +0200

    Undo spaces

commit 5f8a9636c4a5cd1842aac01e3fece5eef6a0b996
Author: Marten Veldthuis <marten@veldthuis.com>
Date:   Mon Sep 29 15:45:19 2014 +0200

    Rename started_completing_at to started_at

commit d128db3533381be5234339476451c51e3134ebaa
Author: Marten Veldthuis <marten@veldthuis.com>
Date:   Fri Sep 26 11:10:10 2014 +0200

    Feature does not always work within feature?

commit cf82d0367e65ac66b1713c8dbad52817ba159600
Author: Marten Veldthuis <marten@veldthuis.com>
Date:   Fri Sep 26 11:07:08 2014 +0200

    Add started_completing_at