additional test coverage for HatsIdUtilities library

[spengrah]

#58 refactored functions related working with hat ids into a library to be inherited into Hats.sol. This makes the contract more readable, and it also has the benefit of making those functions more readily available by other developers.

With that in mind, its important to ensure that the library works across a wider array of test cases than are narrowly required for Hats.sol alone.