preserves 4.995.2

Implementation of the Preserves serialization format via serde.
Documentation 
@<EmacsMode "-*- preserves -*-">
[
  <Apple <Colour "red">>
  <Peach>
  <Apple <Colour "green">>
  <Banana <kilograms 0.12> <Colour "brownish"> 5 {ripeness: <Squishy>}>
  <Pear <Conference>>
]