Fix Memcached Launchd plist label collision.
Fix Memcached continually attempting to restart.

Repeating in system log:
(org.memcached.memcached): Throttling respawn: Will start in 10 seconds
Update Create Folders step to include /usr/local/var and /usr/local/var/log.
Add instructions for Redis.
Update Launchd text.
Update Memcached terminology.
Update Shell section intro text.