Robust new OID codec registration
At the moment there is only small subset of supported type conversions between PicoLisp program and PostgreSQL backend. Probably there should be procedural way to register new codecs in order to support more types.
For example:
(load "pg.l")
(load "json.l")
(setq json-decode decode)
(pg-start ...)
(pg-register-codec "jsonb" json-decode)
...
(pg-execute "SELECT jsonb_build_object('key', 'value');")
# -> ((("key" . "value")))
...
(pg-finish)