Add hiredis-0.11.0

Hiredis is a minimalistic C client library for the Redis database.

It is minimalistic because it just adds minimal support for the
protocol, but at the same time it uses an high level printf-alike
API in order to make it much higher level than otherwise suggested
by its minimal code base and the lack of explicit bindings for
every Redis command.

Apart from supporting sending commands and receiving replies, it
comes with a reply parser that is decoupled from the I/O layer. It
is a stream parser designed for easy reusability, which can for
instance be used in higher level language bindings for efficient
reply parsing.

Hiredis only supports the binary-safe Redis protocol, so you can
use it with any Redis version >= 1.2.0.

The library comes with multiple APIs. There is the synchronous API,
the asynchronous API and the reply parsing API.
add hiredis
Added databases/hiredis version 0.11.0
Add two new options for exim:
	- exim-lookup-redis: allow quering redis from within the exim
	                     config, needs hiredis
	- opendmarc: enables DMARC support
Both are disabled by default.