Create pure interface for Address type.

[Mokosha]

Currently, in the high level bindings we store the address type using a ForeignPtr. This is fine, since the C library may have different representations in memory. It has the unfortunate wart of requiring all interfaces that take an Address to be in the IO monad though. It would likely be cleaner to interpret the memory representation into a high-level datatype. Probably something that looks like this:

newtype IPv4Address = IPv4Address (Word8, Word8, Word8, Word8)
  deriving (Eq, Ord, Show, Read, Bounded)
newtype IPv6Address = IPv6Address (Word16, Word16, Word16, Word16, Word16, Word16, Word16, Word16)
  deriving (Eq, Ord, Show, Read, Bounded)

data Address = Address'IPv4 !Word16 !IPv4Address
             | Address'IPv6 !Word16 !IPv6Address
  deriving (Eq, Ord, Show, Read, Bounded)

After this change, the only functions that need IO will be those that convert between memory representations and Haskell (like parseAddress). Others (like the Eq typeclass or addressPort) will not.