Add support for PostgreSQL's JSON[B]

[nkonev]

Resolves #920

[nkonev]

@schauder Could you review it ?

[schauder]

We discussed the issue of JSON support internally. We want to give it a more complete treatment that will eventually allow a more powerful usage, like referencing parts of the resulting JSON in queries.

For this we might use your PR, that's why I'd like to keep it open, although we won't merge it as it is right now.

For the issue #920 it would be sufficient to make PGObject a simple type for the Postgres dialect.

[nkonev]

@schauder

For the issue #920 it would be sufficient to make PGObject a simple type for the Postgres dialect.

Ok, than you for reply, I gonna do a small PR with only PGObject

[mp911de]

Closing this pull request in favor of a properly designed JSON integration that supports pluggable JSON libraries and dialect-specific support for JSON path queries/projections.

[mp911de]

See also #1008