Updating the code to keep up with the changes to scotty

Scotty 0.6 has introduced custom exception types and the change is
reflected in this update. The main types are now polymorphic over an exception type

    type ScottyH e = ScottyT e HState
    type ActionH e = ActionT e HState

In addition, the specialized (to `Text`) types and runners are
introduced

    type ScottyH' = ScottyH Text
    type ActionH' = ActionH Text
    scottyH'     :: Port -> ScottyH' () -> IO ()
    scottyHOpts' :: Options -> ScottyH' () -> IO ()

Thanks to Kirill Zaborsky for pointing out the incompatibility with 0.6.
Updating the changelog