Adds getters and setters for `bool` to the `Storage` library
as well as the `StorageSetter` contract. The tests happen through
the `StorageSetter` contract for simplicity. The `StorageSetter`
contract is important for the production 2 step upgrade process where
the storage migrations are decoupled from `initialize()`.

Also update the `StorageSetter` to use named return args per the latest
changes to the Solidity style guide.