Features that sooner or later will be added to `ngx_postgres`:

* Make sure that we work-around `bytea` data corruption that takes place

when using 9.0+ database with older client library or vice-versa.

* Add support for SSL connections to the database.

* Add support for dropping of idle keep-alived connections to the

database.

* Add support for sending mulitple queries in one go (transactions,

multiple SELECTs, etc), this will require changes in the processing

flow __and__ RDS format.

* Add `postgres_escape_bytea` or `postgres_escape_binary`.

* Use `PQescapeStringConn()` instead of `PQescapeString()`, this will

require lazy-evaluation of the variables after we acquire connection,

but before we send query to the database.

Notes: Don't break `$postgres_query`.

* Cancel long-running queries using `PQcancel()`.

* Detect client library version using `PQlibVersion()` (PostgreSQL 9.1+)

or exports (for older releases):

8.0.0 -> PQcancel 122

8.1.0 -> PQregisterThreadLock 125

8.1.4 -> PQescapeByteaConn 127

8.2.0 -> PQsendDescribePortal 136

8.3.0 -> PQconnectionNeedsPassword 140

8.4.0 -> PQinitOpenSSL 153

8.5.x -> PQinitOpenSSL 153

9.0.0 -> PQconnectStartParams 157

9.1.x -> PQlibVersion 160

* Detect server version using `PQserverVersion()`.