UTF-8 validation when deserializing

[kolmodin]

As pointed out in #70 by @ttuegel we don't do validation of UTF-8 when decoding. This needs to be fixed.

Consider introducing getList in Binary if it makes a big difference for performance. With getList we could use some of the faster UTF-8 validators without having to write our own. See how text does utf8 validation . Our case might be more difficult though as we don't know beforehand whether all input bytes are available.

class Binary a where
  -- ...
  getList :: [a]
  getList = getDefaultList

getDefaultList :: Binary a => Get [a]
getDefaultList = get >>= getMany

class Binary Char where
  -- ...
  getList = -- faster code