Add try operator

[kritzcreek]

Could we add a try operator like Control.Exception has in Haskell? I'm currently using this:

try ∷ ∀ a e. Eff (err ∷ EXCEPTION | e) a → Eff e (Either Error a)
try action = catchException (pure ∘ Left) (Right <$> action)

The only problem would be that this introduces a dependency on purescript-either.

[garyb]

I don't think having that dependency would be a problem. What say you @paf31?

[paf31]

Sounds good to me.

[kritzcreek]

Fixed with #16