Add default implementation for Bits.bitSize
I think it would be a good idea to provide a default implementation for bitSize, example:
bitSize b = fromMaybe (error "bitSize is undefined") (bitSizeMaybe b)
The advantage is that from now on new instances of Bits no longer need to define bitSize.
And once bitSize has been removed there will be no errors about it not being a method of class Bits.