2.0.0

CHANGES:

• [breaking] Library, PPX: Unify runtimes (*.ppx-runtime libraries are
  removed, can use melange-json and melange-json-native instead), replace
  Json module with Melange_json, deprecate Decode and Encode modules,
  introduce new decoding error type and helper function
  of_json_error_to_string.
  (#36)
• [breaking] PPX: Code to decode polyvariants doesn't use an additional
  _poly function which was also generated by the PPX. Instead
  Unexpected_variant error is used to signal that next decoder should be
  tried. (#32)
• [breaking] Json.Decode.DecodeError exception now contains a variant type
  as payload instead of a string.
  (#32)
• [breaking] PPX: Rename [@json.as] to [@json.name]
  (#23)
• [breaking] PPX: Drop special encoding for enumeration-like variants
  (variants with each constructor having no arguments).
  (#26)
• [breaking] PPX: change JSON representation of polyvariants, make it
  compatible with ppx_deriving_yojson and ppx_yojson_conv
  (#27)
• [breaking] PPX: Consistent use of exceptions in runtime.
  (#28)
• PPX: [@@deriving json] now can be used within signatures (this includes
  .mli files).
  (#32)
• PPX: Add runtime for result
  (#13)
• PPX: Add yojson as runtime dep for the native version
  (#15)
• PPX: add [@@json_string] for deriving converters to/from JSON strings
  directly (#30)
• PPX: add support for int64 in the runtime
  (#33)
• PPX: remove string_to_json usage on js side
  (#35)
• PPX: Add array functions to native runtime
  (#37)