breakRetainCycle: Break retain cycle in bind(to:input:)

[nflahavan]

#227

This pull request breaks the retain cycle in the various bind(to:input:) methods. Tests have also been added to ensure no retain cycle is introduced by calling bind(to:input:).

[bobgodwinx]

sounds like a plan @nflahavan Thanks for spotting it out.. 👍🏾

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