sss/open-union: add Typeable instances

for ghc-7.8 and above we're able to have Typeable instances both for
'Union' and ':>' since Typeable is now poly-kinded.

we should now be able to, say use, 'Eff' as a type of State for GHC
versions 7.8 and above

sss/eff: update README to reflect current status wrt Typeable
sss/eff: version bump: 1.8.0.0 -> 1.8.1.0