Use method_missing instead of SimpleDelegator.

SimpleDelegator requires the delegate object to correctly implement
respond_to?(). That isn't always the case, so best to simply delegate
all methods regardless of whether or not the delegate object responds to
them.
Redis::WithScriptCaching now defaults to Redis.new

'Cause hey, why not.
Test on Ruby 2.0 as well.

More coverage, less problems.