Make it possible to specify a custom strategy for redis-cluster.
Add method to get connection factory from redis-cluster connection.
Remove useless method.

It is better to wrap explicitly a multibulk response iterator into a
multibulk tuple response iterator instead of hard-coding that into a
specialized method.
Fetch cluster slots from node upon first -MOVED response.

This is a more sane default as it allows users to indicate only a few
servers of the whole cluster composition, while it previously required
a more complex configuration of the client using client options.

This feature can be disabled using the "enableAutoSlotsMap()" method.
Minor phpdocs fixes.

[ci skip]
Fetch updated slots map from node indicated by -MOVED response.

This optimization makes it possible to fetch the slots map directly
from the server indicated by the -MOVED response eliminating the need
to use a random node in the pool, which in turn could require Predis
to open a new and useless connection.
Fix phpdocs.
Rename method "enableAutoSlotsMap()" to "useClusterSlots()".