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.
Set the right order to parse the redis info.
Add memory_lua data type
Support the switch from credis to hiredis