Add RBS definitions via sord

[dorner]

Add YARD comments so we can run sord on the codebase.

This is using my fork of sord that has the --hide-private feature: https://github.com/AaronC81/sord/pull/146

[codeclimate[bot]]

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[jenchanflipp]

Two of the checks are failing - should they be passing?

[dorner]

This is part of the CI issues we're having - Travis keeps segfaulting. If you click into it you'll see that it passes on one version of Ruby but fails on the other two. Angad is looking into this part.