Proposal: Remove Num superclass of Bits

[John Meacham]

Or even worse,

if 3 then True else False  would result in 'False' since 3 /= true (1)
or 'True' since 3 /= false (0)

neither is obvious.

Adding just zero and one doesn't completely solve the problem, because
testBit uses equality with zero, so an Eq instance is needed.

I would just remove the bit and testBit defalut instances, they seem
like reasonable primitives to be required for an instance.

    John