This adds deprecations in preparation for `pg@7.0`
- deprecate using event emitters on automatically created results from client.query.
- deprecate query.promise() - it should never have been a public method and it's not documented. I need to do better about using _ prefix on private methods in the future.
- deprecate singleton pool on the `pg` object. `pg.connect`, `pg.end`, and `pg.cancel`.
b5b49eb895