Switch redis.c plugin from credis to hiredis.

Change the entire redis.c plugin to use libhiredis (tested with
libhiredis0.10) instead on credis. The libhiredis is supported in a number
of distributions like Debian or Ubuntu.

This patch keeps the same functionality that the old redis.c does.
use timeval. keep timeout in milliseconds for backwards compatibility.
Revert types for redis.c plugin.
remove all credis left. Migrate write_redis too.
Merge pull request #3 from linuxmaniac/write_redis_hiredis

Migrate write_redis to hiredis
Set the right order to parse the redis info.
Add memory_lua data type
Merge pull request #4 from ganguera/hiredis-without-custom-query

Set the right order to parse the redis info.
Fix memory leak in redis.c
Merge pull request #5 from mspiegle/hiredis-without-custom-query

Fix memory leak in redis.c
Merge pull request #1 from ajdiaz/hiredis-without-custom-query

Hiredis without custom query