"An arithmetic shift is usually equivalent to
multiplying the number by a positive or a negative
integral power of the radix." -- Federal Standard 1037C
"This is the same as multiplying x by 2**y."
"A right shift by n bits is defined as floor division
by pow(2,n). A left shift by n bits is defined as
multiplication with pow(2,n)."
This is because Haskell defines negate, abs and signum
for Num, but they don't work with our unsigned number
types. (abs would be a noop.) Haskell has Word32 / Word64,
but there negate doesn't make much sense to me.
Implemented neg and abs.
Implemented a type class inheritance check.
Removed Integral from u8 and i8 since it wasn't implemented.
