Escape double '??' to a literal '?'

[Vlix]

This change makes it possible to use literal question marks in queries to PostgreSQL. This is needed to be able to use the new JSON operators. https://www.postgresql.org/docs/9.5/static/functions-json.html

This change can't break anything, since:

• Anyone using double question marks would get an error from postgresql-simple if not supplied the adequate amount of accompanying Actions (e.g. people trying the new JSON operators); or

• If supplied the adequate amount of accompanying Actions, PostgreSQL would throw a fit because you'd supply two values directly next to each other, which doesn't make sense.

[Vlix]

Anyone know how often @lpsmith checks this repository?

[Vlix]

The tests here use PSQL version 9.4 since that's when jsonb and the question mark operators got introduced. If it's needed to keep testing postgresql-simple on version 9.3, I can make changes so the tests are only run on a seperate test that uses a PSQL version higher than 9.3

[Vlix]

Bump.

Doesn't anyone want to use JSON operators in PostgreSQL?

[phadej]

@Vlix sorry for not noticing, I haven't watched this repository closely. If you mind making PR against my fork, it would help (there's up to date travis setup as well)

[Vlix]

@phadej Ah, hadn't noticed the maintainer has switched. Will do.