Major changes include support for JSON encoding and providing compatibility
with OCaml 3.12.0.
Piqi tools:
- "piqi convert" command now supports two new encodings: "json" (plain JSON)
and "piq-json" (JSON with Piq type annotation for top-level objects).
- A new command: "piqi json-pp" for pretty-printing JSON files.
Piqi language:
- Added support for "json-name" property for type definitions, fields and
options. When specified, it will be used as a name for correspondent JSON
field names instead of "name".
- Renamed "ignore-field" top-level directive to "custom-field".
Other changes:
- Provided compatibility with the latest OCaml release (3.12.0). Improved
support for older OCaml versions >= 3.10.
