Added story#add_owner

[forest]

This might be an acceptable compromise to not supporting << for owner_ids. Also consistent with the add_label interface which exists for the same reasons.

[forest]

@drselump14 how does this look? Not << but much clearer interface.

[coveralls]

Coverage increased (+0.06%) to 96.534% when pulling 14fee7a on add-owners into fbbb085 on master.

[drselump14]

@forest it's fine I guess ... consistent with what stated on readme

[forest]

@drselump14 feel free to take a stab at implementing <<. I'm not against it, but it wasn't worth the effort for me. I haven't dug in too deep yet, but some of the http://dry-rb.org/gems gems could be used to replace Virtus and might make this easier. It would be a huge rewrite. From what I have read dry-rb gems are the next generation of Virtus.