Implements pattern binds

[anton-k]

It's possible to write code with pattern binds for high-level language:

 data User = User Text Int

 (bs, pair) = getArgs
 john = User "john" 10
 User name _ = john

 main =
   let (a, b) = pair
   in  appendBytes (appendBytes (sha256 bs) (serialise (a + b + c + age  + lengthText name))) d
   where
     (c, d) = getBoxArgs getSelf
     (User _ age) = john