Make doctests work for multiline docs

[wende]

Right now the docests will work only if

1. They are in a single new line
2. They have a == equation at the top

While it covers about 70% of the cases, it would be nice to be able to write tests which are multiline, where only the last one is a test, and previous ones are setups.

Example:

{- Maps a function

    f = (+) 1          -- These two should be
    list = [1, 2, 3]   -- put under let..in
    myMap f list == [2, 3, 4]  -- this is the final test

    myMap ((*) 2) list -- This is a second test
-}
myMap : (a -> b) -> List a -> List b
myMap f list =
  case list of
    [] -> []
    x :: xs -> f x :: myMap f xs