morloc-project/morloc: Guarded recursion

The commit adds guards and recursion. Direct recursion: fact :: Int -> Int fact n ? n == 0 = 1 : n * fact (n - 1) Mutual recursion: isEven :: Int -> Bool isEven n ? n == 0 = True : isOdd (n - 1) isOdd :: Int -> Bool isOdd n ? n == 0 = False : isEven (n - 1) Guards can be used at function level, in let statements, and inline.